THE NEW THEORY OF HEREDITY.
(A Synopsis.) By Surgeon W. J.
BUCHANAN, b.a.,
m.b.
Any one who has read the discussions in the section of psychology at the late meeting of the British Medical Association must have been struck by tlie extremely vague views on the subject of heredity possessed by the speakers. One speaker, indeed, went so far as to question the truth of the idea of heredity; none of the others showed that their knowledge rose above certain popular notions about inheritance. On reading this, it seemed that it might be useful and interesting to the readers of this paper if a brief and accurate account of the latest views 011 the subject were given. We see too often in medicine how the idea of heredity is evoked as an etiological factor in many diseases. In cancer or leprosy for example, heredity is claimed by some to be all-powerful, while others deny In view of the new theory its influence in toto. to which we refer, the whole question of the inheritance of disease will have to be reconsidered. I hope at some future time to be able to attack that subject, at present the subject will only bo sketched in its purely biological aspect. In a review in these columns some months ago this subject was briefly touched upon. The theory I am now about to synopsize is that of Prof. Weismann,of Frieberg. It is curious how little attention has been paid to these
views, revolutionary though they
are,
except by
If this theory is true, it is the contribution to biology and evolution since the publication of Darwin's Origin of Species. Till this view is thoroughly grasped, it is mere waste of time to speculate how far disease is capable of being transmitted from the
biologists. most important
parent
to
offspring.
The problem of heredity is one which has Its phenomena hitherto baffled investigation. It is are not in their nature incomprehensible. only the great complexity of the subject which has till now rendered it insuperable.
Heredity in its common acceptation may be defined as that property of an organism by which its peculiar nature is transmitted to its descenFrom an eagle's egg an eagle of the dants. Not only are the charsame species developes. acters of the species transmitted to the following generation, but even individual peculiarities. The offspring resembles its parents among animals as well as man. Heredity can be easily understood in the case of unicellular organisms (infusoria, &c.) They multiply by the simple process of division, each part becoming exactly alike in structure and size. Among multicellular organisms, however, the problem is more difficult. Darwin, it is well-known, by his purely formal and provisional hypothesis of Pangenesis
Jan.
BUCHANAN ON A NEW THEORY OF HEREDITY.
1892.]
attempted
to
explain
the
phenomena, thereby
reviving great extent the oldest theory, that of Democritus. Brook's theory went still further to
a
in throwing light upon the matter, but it was reserved for Prof. VVeismann to put forward a well reasoned and carefully investigated hypothesis which seems to have reached the truth at last. What this theory is will now be explained, Weismann begins by asking how it is that a single cell of the body can contain within itself all the hereditary tendencies of the whole organism. To this question ho considers only two answers are physiologically possible : first, that the substance of the parent germ-cell is capable of undergoing a series of changes which, after the building up of a new individual, leads back again to identical germ-cells, or the germ-cells are not derived at all, as far as their essential and characteristic substance is concerned, from the body of the individual, but they are derived directly from the parent germ-cells. The latter he believes to be the true answer. He has called this " the theory of the continuity of the germcell," for it is founded on the idea that heredity is brought about by the transference from one generation to another of a substance with a definite chemical and above all molecular substance which he calls the germ-plasm. He assumes that it possesses a highly complex structure conferring 011 it the power of developing into a complex organism. He explains heredity by supposing tliat in each production of a being (ontogeny) a part of the specific germ-plasm contained in the parent egg-cell is not used up in the construction of the body of the offspring, but is reserved unchanged for the Formation of the germ-cells of the following generation. Hence as the germ cells of successive generations are directly continuous and form as it were only different parts of the same substance, it follows that these cells must or at least may possess the same molecular constitution, that they would therefore pass through the same stages of development and would form the same final product. From this it follows that the transmission of characters acquired during one individual's lifetime is an impossibility, for, if the germ-plasm is derived from that which preceded it, its structure find molecular constitution cannot depend upon the indviidual in which it happens to occur, for the individual forms, as it were, only the soil in which the germ-plasm grows, while the latter possesses its characteristic structure from the beginning, i.e., before the commencement of growth. As the tendencies of heredity depend upon this very molecular structure, only those characters can be transmitted through successive generations which have been previously inherited, viz., such characters as were potentially contained in the structure of the Therefore such characgerm-plasm. ters as have been acquired by special external
the lifetime of the parent cantransmitted. By " acquired " characters should be understood those which first appear in the body itself, somcttogenetic, as opposed to those
agencies during
not be
their appearance to variations in the blastogenetic. The former cannot be transmitted, they include not only the effects of mutilation, but also the changes which follow from increased use and disuse; and those directly due to nutrition or any external influence among " (i blastogenetic characters are included all the changes produced by natural selection acting on variations in the germ, and such so-called spontaneous characters, as extra fingers, toes, patches of grey hair, moles, &c., which can all be certainly transmitted. This is a very important point not only from its biological interest in necessitating a certain modification of the theory of Darwin, but in its relation to the question of Up till the present the heredity in disease. statement that acquired characters are transmitIt has even ted has been generally accepted. assumed the character of an axiom. So far from being so it is an unproved hypothesis, which has been deduced from the very facts it attempts which
owe
crerm
to
explain.
Let us now endeavour to explain the source of that individual variability upon which the principle of natural selection so entirely depends and without which it could not exist. How, it may be asked, can such hereditary individual characters exist if changes wrought by the action of external circumstances during the life of an individual cannot be transmitted? Weismann believes such ati explanation is to be found in that form of reproduction by which the majority of organisms are propagated, viz., sexual. This process consists essentially in the coalescence of These two distinct germ-cells or their nuclei. germ-cells contain the germ-plasm which is the bearer of the hereditary tendencies of the organism. Therefore in sexual reproduction two groups of hereditary tendencies are combined. Let us now go further back and see what light embryology can throw on this point. It has been demonstrated that the egg of every animal, which has been examined by our modern highly efficient means of search, produces at least two bodies known as " polar bodies." It has been shown by Weismann and others that two polar bodies are expelled as a preparation for embryonic development from all animal eggs which require fertilization. In Weismann's opinion the expulsion of the first polar body implies the removal of the ovogenetic nucleoplasm which has become superfluous after the maturation of The expulsion of the egg has been completed. the second polar body can only mean the removal of a part of the germ-plasm itself, a removal by which the number of ancestral germ-plasms is reduced to one-half. This reduction must also take place in the male germ-cells, though we are ?
?
INDIAN MEDICAL GAZETTE. associate it confidently with any of the histological processes of spermatogenesis hitherto observed. Development, by fertilization makes it necessary that half the number of these ancestral germ-plasms must first be expelled from the egg; the original quantity being again restored by the addition of the sperm necleus to the remaining half, for, in the union of these two, there is a double combination of aucestral tendencies. Now, as even in ten generations there is a mixture of 1,024 ancestors, it is obvious that such a minute subdivision of the continuous germ-plasm could not go on for ever. Therefore, at each coalescence of these cells the number of ancestral units is reduced in each to one-half. But in such a complex body as the nuclear substance of the egg-cell, composed as it is of innumerable different units,it is hardly conceivable that the process " of haryokinesis or es reducing division could in ever twice take place exactly the same way, hence the germ-cells of the same mother cannot contain the same hereditary tendencies, and the offspring of the same mother can never be exactly identical, that is, each will possess some This explanation will individual difference. render intelligible the fact that children of the same parents are never entirely identical. Additional probability is added to this view when we consider the case of twins. The well-known anthropologist Galton has investigated a series In some of cases of close similarity in twins. cases the two children, generally of the same sex, are so similar in appearance, tastes, and dispositions that strangers and even parents often fail to distinguish between them ; as Galton says, "they continue their lives, keeping time like two watches, hardly to be thrown out of accord except by some physical jar." There are also twins which do not possess this high degree of similarity, iudeed they are the more common. The difference seems to be that in the former case the twins are derived from the same egg, from the same combination of ancestral tendencies ; in the latter case, it is almost certain they are derived from two egg-cells which were fertilized at the same time. Let us now return to the question of acquired It is well-knownhow Lamark imacharacters. he explained the transformation of species. gined He taught that a change in the structure of an organism was chiefly brought about when the species met with new conditions of life and was thus forced to assume new habits. Such habits caused increased or diminished activity, and a stronger or weaker development of certain parts, which parts he supposed were transmitted, thus modified, from parent to offspring, which modifications, he thought,were transmitted and increased in each successive generation till the greatest possible change had been effected. For example, he attributed the long neck of swans and other not able to
[Jan.
1892.
animals to the habit of stretching after food at the bottom of the water. The disappearance of parts after they had ceased to be of use was similarly explained, e.g., the degeneration of the No eyes of animals inhabiting dark caves. attempt^ except in the case of apparently transmitted mutilations, was made to prove this as-
sumption. Now, if we premise the truth of Weismann's theory, it is obvious that we must explain these
facts in some other way. This may be done as follows :?In the first place, we may urge that if an organ becomes stronger by exercise, it must possess a certain amount of importance in the life of the individual, uul if so, it becomes subject But the perto the action of natural selection. fection of an organ depends primarily and chiefly upon the fact that the germ from which the individual arose was predisposed to produce a perfect organ. We cannot by feeding make a giant out of a germ destined to become a dwarf, nor by exercise transform the muscles of an individual destined to be feeble into those of a Hercules, nor the brain of a predestined fool The into that of a Newton or a Darwin. increase of an organ in the course of generations does not depend upon the summation of exercise taken during single lives, but on the summation of more favourable predispositions in the germs. When any change in environment compels any organ to be more largely used, each individual will endeavour to accommodate itself to the best of its power. How far it can do so depends upon the predisposition of the germ, so that natural selection while it apparently decides between individuals of various strengths in reality operates 011 the stronger and weaker germs. To take next the cases of atrophy after disuse. Here, again,is a case of ability and natural selection. Darwin himself has shown how it is an advantage for many beetles in the island of Madeira to have lost their wings. This degeneration would be favoured by natural selection. So also can be explained the loss of limbs in snakes, &c., who live in holes and narrow clefts of rocks. But when the degeneration of disused confers no benefit upon the individual organs the explanation becomes less simple. For example, the eyes of animals which inhabit dark caves have degenerated, but tliey could live quite as well in the dark with fully developed eyes. This brings up to an important aspect of natural selection, viz., the power of conservation exerted by it. " Not only does the survival of the fittest select the best but it also maintains it." For example, it maintains the keenness of sight of birds of prey, for any one born with less keen sight would be at a disadvantage compared with its fellows, and could not in the long run escape death from hunger. But suppose such birds were compelled to live in a dark cave, the quality of the vision would then become immaterial,
Jan.
FINK'S CASE OF RUPTURE OF SMALL INTESTINE.
1892.]
sind if weaker eyes arose from time to time these might be transmitted, for their imperfection would bring no disadvantage to the owner. Hence by crossing individuals of varied degrees of sight, the average of perfection would slowly Another factor to be considered is what decline. Roux has called " the struggle of the parts in Cases of atrophy after disuse an organism." are attended with a corresponding increase in other organs, blind animals always possess well developed organs of touch, hearing, or smell. Thus the cessation of the action of natural selection on a useless organ will tend to make it degenerate, while its action on useful organs will further reduce the disappearing organ as the latter take the place and nutriment of more important parts. Natural selection will thus encourage the weaker development of a useless part till the germ has lost all tendency to the production of the organ in question. The extreme slowness with which this process works is shown by the persistence of what are called rudimentary structures. This principle of the suspension of the conserving influence of natural selection Weismanu has called "Panmixia." We may illustrate it by another example, the case of shortsightedness so common among civilized nations. This has been explained as an example of the transmission of acquired characters, but we must remember that the refraction of the human eye has been long independent of natural selection. Myopia does not prevent a civilized man from earning his living. These fluctuations on either side of normal vision are due to the same causes as operate in producing the degeneration of the eyes of cave-dwelling animals. Where in some families myopia is hereditary, it is due to an accidental disposition of the germ. Beside, it is probable that a large number of shortsighted people have acquired this defect for themselves.- Again, the well-known greater variability of domestic animals depends essentially upon this principle. A duck or a goose must possess strong powers of flight in the natural state, but when brought to a poultryyard, the rigid selection of birds with well developed wings is 110 longer needed, and a deterioration will necessarily ensue. We have not here space to go into the interesting and important question of heredity in genius or of particular talents, nor can we touch upon the question of the alleged transmission of multilatious. Suffice it to say that an unbiassed investigation of all cases of supposed transmission of mutilations shows that the evidence in support is- in every cases faulty, notwithstanding the efforts of Prof. Eimer and his followers to establish it. We have thus as briefly as possible iudicated what the new theory of heredity is. Time and further research will determine to what extent it is true. o
o
(A Synopsis.) By Surgeon W. J.
BUCHANAN, b.a.,
m.b.
Any one who has read the discussions in the section of psychology at the late meeting of the British Medical Association must have been struck by tlie extremely vague views on the subject of heredity possessed by the speakers. One speaker, indeed, went so far as to question the truth of the idea of heredity; none of the others showed that their knowledge rose above certain popular notions about inheritance. On reading this, it seemed that it might be useful and interesting to the readers of this paper if a brief and accurate account of the latest views 011 the subject were given. We see too often in medicine how the idea of heredity is evoked as an etiological factor in many diseases. In cancer or leprosy for example, heredity is claimed by some to be all-powerful, while others deny In view of the new theory its influence in toto. to which we refer, the whole question of the inheritance of disease will have to be reconsidered. I hope at some future time to be able to attack that subject, at present the subject will only bo sketched in its purely biological aspect. In a review in these columns some months ago this subject was briefly touched upon. The theory I am now about to synopsize is that of Prof. Weismann,of Frieberg. It is curious how little attention has been paid to these
views, revolutionary though they
are,
except by
If this theory is true, it is the contribution to biology and evolution since the publication of Darwin's Origin of Species. Till this view is thoroughly grasped, it is mere waste of time to speculate how far disease is capable of being transmitted from the
biologists. most important
parent
to
offspring.
The problem of heredity is one which has Its phenomena hitherto baffled investigation. It is are not in their nature incomprehensible. only the great complexity of the subject which has till now rendered it insuperable.
Heredity in its common acceptation may be defined as that property of an organism by which its peculiar nature is transmitted to its descenFrom an eagle's egg an eagle of the dants. Not only are the charsame species developes. acters of the species transmitted to the following generation, but even individual peculiarities. The offspring resembles its parents among animals as well as man. Heredity can be easily understood in the case of unicellular organisms (infusoria, &c.) They multiply by the simple process of division, each part becoming exactly alike in structure and size. Among multicellular organisms, however, the problem is more difficult. Darwin, it is well-known, by his purely formal and provisional hypothesis of Pangenesis
Jan.
BUCHANAN ON A NEW THEORY OF HEREDITY.
1892.]
attempted
to
explain
the
phenomena, thereby
reviving great extent the oldest theory, that of Democritus. Brook's theory went still further to
a
in throwing light upon the matter, but it was reserved for Prof. VVeismann to put forward a well reasoned and carefully investigated hypothesis which seems to have reached the truth at last. What this theory is will now be explained, Weismann begins by asking how it is that a single cell of the body can contain within itself all the hereditary tendencies of the whole organism. To this question ho considers only two answers are physiologically possible : first, that the substance of the parent germ-cell is capable of undergoing a series of changes which, after the building up of a new individual, leads back again to identical germ-cells, or the germ-cells are not derived at all, as far as their essential and characteristic substance is concerned, from the body of the individual, but they are derived directly from the parent germ-cells. The latter he believes to be the true answer. He has called this " the theory of the continuity of the germcell," for it is founded on the idea that heredity is brought about by the transference from one generation to another of a substance with a definite chemical and above all molecular substance which he calls the germ-plasm. He assumes that it possesses a highly complex structure conferring 011 it the power of developing into a complex organism. He explains heredity by supposing tliat in each production of a being (ontogeny) a part of the specific germ-plasm contained in the parent egg-cell is not used up in the construction of the body of the offspring, but is reserved unchanged for the Formation of the germ-cells of the following generation. Hence as the germ cells of successive generations are directly continuous and form as it were only different parts of the same substance, it follows that these cells must or at least may possess the same molecular constitution, that they would therefore pass through the same stages of development and would form the same final product. From this it follows that the transmission of characters acquired during one individual's lifetime is an impossibility, for, if the germ-plasm is derived from that which preceded it, its structure find molecular constitution cannot depend upon the indviidual in which it happens to occur, for the individual forms, as it were, only the soil in which the germ-plasm grows, while the latter possesses its characteristic structure from the beginning, i.e., before the commencement of growth. As the tendencies of heredity depend upon this very molecular structure, only those characters can be transmitted through successive generations which have been previously inherited, viz., such characters as were potentially contained in the structure of the Therefore such characgerm-plasm. ters as have been acquired by special external
the lifetime of the parent cantransmitted. By " acquired " characters should be understood those which first appear in the body itself, somcttogenetic, as opposed to those
agencies during
not be
their appearance to variations in the blastogenetic. The former cannot be transmitted, they include not only the effects of mutilation, but also the changes which follow from increased use and disuse; and those directly due to nutrition or any external influence among " (i blastogenetic characters are included all the changes produced by natural selection acting on variations in the germ, and such so-called spontaneous characters, as extra fingers, toes, patches of grey hair, moles, &c., which can all be certainly transmitted. This is a very important point not only from its biological interest in necessitating a certain modification of the theory of Darwin, but in its relation to the question of Up till the present the heredity in disease. statement that acquired characters are transmitIt has even ted has been generally accepted. assumed the character of an axiom. So far from being so it is an unproved hypothesis, which has been deduced from the very facts it attempts which
owe
crerm
to
explain.
Let us now endeavour to explain the source of that individual variability upon which the principle of natural selection so entirely depends and without which it could not exist. How, it may be asked, can such hereditary individual characters exist if changes wrought by the action of external circumstances during the life of an individual cannot be transmitted? Weismann believes such ati explanation is to be found in that form of reproduction by which the majority of organisms are propagated, viz., sexual. This process consists essentially in the coalescence of These two distinct germ-cells or their nuclei. germ-cells contain the germ-plasm which is the bearer of the hereditary tendencies of the organism. Therefore in sexual reproduction two groups of hereditary tendencies are combined. Let us now go further back and see what light embryology can throw on this point. It has been demonstrated that the egg of every animal, which has been examined by our modern highly efficient means of search, produces at least two bodies known as " polar bodies." It has been shown by Weismann and others that two polar bodies are expelled as a preparation for embryonic development from all animal eggs which require fertilization. In Weismann's opinion the expulsion of the first polar body implies the removal of the ovogenetic nucleoplasm which has become superfluous after the maturation of The expulsion of the egg has been completed. the second polar body can only mean the removal of a part of the germ-plasm itself, a removal by which the number of ancestral germ-plasms is reduced to one-half. This reduction must also take place in the male germ-cells, though we are ?
?
INDIAN MEDICAL GAZETTE. associate it confidently with any of the histological processes of spermatogenesis hitherto observed. Development, by fertilization makes it necessary that half the number of these ancestral germ-plasms must first be expelled from the egg; the original quantity being again restored by the addition of the sperm necleus to the remaining half, for, in the union of these two, there is a double combination of aucestral tendencies. Now, as even in ten generations there is a mixture of 1,024 ancestors, it is obvious that such a minute subdivision of the continuous germ-plasm could not go on for ever. Therefore, at each coalescence of these cells the number of ancestral units is reduced in each to one-half. But in such a complex body as the nuclear substance of the egg-cell, composed as it is of innumerable different units,it is hardly conceivable that the process " of haryokinesis or es reducing division could in ever twice take place exactly the same way, hence the germ-cells of the same mother cannot contain the same hereditary tendencies, and the offspring of the same mother can never be exactly identical, that is, each will possess some This explanation will individual difference. render intelligible the fact that children of the same parents are never entirely identical. Additional probability is added to this view when we consider the case of twins. The well-known anthropologist Galton has investigated a series In some of cases of close similarity in twins. cases the two children, generally of the same sex, are so similar in appearance, tastes, and dispositions that strangers and even parents often fail to distinguish between them ; as Galton says, "they continue their lives, keeping time like two watches, hardly to be thrown out of accord except by some physical jar." There are also twins which do not possess this high degree of similarity, iudeed they are the more common. The difference seems to be that in the former case the twins are derived from the same egg, from the same combination of ancestral tendencies ; in the latter case, it is almost certain they are derived from two egg-cells which were fertilized at the same time. Let us now return to the question of acquired It is well-knownhow Lamark imacharacters. he explained the transformation of species. gined He taught that a change in the structure of an organism was chiefly brought about when the species met with new conditions of life and was thus forced to assume new habits. Such habits caused increased or diminished activity, and a stronger or weaker development of certain parts, which parts he supposed were transmitted, thus modified, from parent to offspring, which modifications, he thought,were transmitted and increased in each successive generation till the greatest possible change had been effected. For example, he attributed the long neck of swans and other not able to
[Jan.
1892.
animals to the habit of stretching after food at the bottom of the water. The disappearance of parts after they had ceased to be of use was similarly explained, e.g., the degeneration of the No eyes of animals inhabiting dark caves. attempt^ except in the case of apparently transmitted mutilations, was made to prove this as-
sumption. Now, if we premise the truth of Weismann's theory, it is obvious that we must explain these
facts in some other way. This may be done as follows :?In the first place, we may urge that if an organ becomes stronger by exercise, it must possess a certain amount of importance in the life of the individual, uul if so, it becomes subject But the perto the action of natural selection. fection of an organ depends primarily and chiefly upon the fact that the germ from which the individual arose was predisposed to produce a perfect organ. We cannot by feeding make a giant out of a germ destined to become a dwarf, nor by exercise transform the muscles of an individual destined to be feeble into those of a Hercules, nor the brain of a predestined fool The into that of a Newton or a Darwin. increase of an organ in the course of generations does not depend upon the summation of exercise taken during single lives, but on the summation of more favourable predispositions in the germs. When any change in environment compels any organ to be more largely used, each individual will endeavour to accommodate itself to the best of its power. How far it can do so depends upon the predisposition of the germ, so that natural selection while it apparently decides between individuals of various strengths in reality operates 011 the stronger and weaker germs. To take next the cases of atrophy after disuse. Here, again,is a case of ability and natural selection. Darwin himself has shown how it is an advantage for many beetles in the island of Madeira to have lost their wings. This degeneration would be favoured by natural selection. So also can be explained the loss of limbs in snakes, &c., who live in holes and narrow clefts of rocks. But when the degeneration of disused confers no benefit upon the individual organs the explanation becomes less simple. For example, the eyes of animals which inhabit dark caves have degenerated, but tliey could live quite as well in the dark with fully developed eyes. This brings up to an important aspect of natural selection, viz., the power of conservation exerted by it. " Not only does the survival of the fittest select the best but it also maintains it." For example, it maintains the keenness of sight of birds of prey, for any one born with less keen sight would be at a disadvantage compared with its fellows, and could not in the long run escape death from hunger. But suppose such birds were compelled to live in a dark cave, the quality of the vision would then become immaterial,
Jan.
FINK'S CASE OF RUPTURE OF SMALL INTESTINE.
1892.]
sind if weaker eyes arose from time to time these might be transmitted, for their imperfection would bring no disadvantage to the owner. Hence by crossing individuals of varied degrees of sight, the average of perfection would slowly Another factor to be considered is what decline. Roux has called " the struggle of the parts in Cases of atrophy after disuse an organism." are attended with a corresponding increase in other organs, blind animals always possess well developed organs of touch, hearing, or smell. Thus the cessation of the action of natural selection on a useless organ will tend to make it degenerate, while its action on useful organs will further reduce the disappearing organ as the latter take the place and nutriment of more important parts. Natural selection will thus encourage the weaker development of a useless part till the germ has lost all tendency to the production of the organ in question. The extreme slowness with which this process works is shown by the persistence of what are called rudimentary structures. This principle of the suspension of the conserving influence of natural selection Weismanu has called "Panmixia." We may illustrate it by another example, the case of shortsightedness so common among civilized nations. This has been explained as an example of the transmission of acquired characters, but we must remember that the refraction of the human eye has been long independent of natural selection. Myopia does not prevent a civilized man from earning his living. These fluctuations on either side of normal vision are due to the same causes as operate in producing the degeneration of the eyes of cave-dwelling animals. Where in some families myopia is hereditary, it is due to an accidental disposition of the germ. Beside, it is probable that a large number of shortsighted people have acquired this defect for themselves.- Again, the well-known greater variability of domestic animals depends essentially upon this principle. A duck or a goose must possess strong powers of flight in the natural state, but when brought to a poultryyard, the rigid selection of birds with well developed wings is 110 longer needed, and a deterioration will necessarily ensue. We have not here space to go into the interesting and important question of heredity in genius or of particular talents, nor can we touch upon the question of the alleged transmission of multilatious. Suffice it to say that an unbiassed investigation of all cases of supposed transmission of mutilations shows that the evidence in support is- in every cases faulty, notwithstanding the efforts of Prof. Eimer and his followers to establish it. We have thus as briefly as possible iudicated what the new theory of heredity is. Time and further research will determine to what extent it is true. o
o
