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ADAPTATION AND INHERITANCE IN THE LIGHT OF MODERN EXPERIMENTAL INVESTIGATION.1

By PAUL KAMMERER, Vienna.

[With 8 plates.]

At the opening of the eighth session of the International Zoological Congress at Graz, in August, 1910, the Graz Tageblatt contained a leading article by Prof. Franz von Wagner, of the University of Graz, the introduction of which ended as follows:

Zoology has expanded tremendously since the publication of Darwin's works, both in breadth and profoundness, and the frail seedling of his day has developed into a sturdy tree with many branches. None of the newer fields of the scientific study of animals illustrate this more convincingly than the steady progress which has been made in recent years in Experimental Zoology. This, as a special study, in the systematic development of methods, has attacked not only the problem of the development of organic form, but has even attempted to solve the riddle of life, striving at the same time to impress upon biology, as far as possible, the stamp of an exact science. It is certainly not through chance that this phase of modern zoology will receive a great amount of attention in the congress at Graz.

During the sessions of the congress, many other individuals expressed similar opinions, among whom a goodly number presented papers or took part in the discussions. Of these there come to mind. men of such note as Appelof, Gadow, and Plate, who emphasized the importance and absolute necessity of basic experimentation. Indeed, we dare not any longer be satisfied simply to observe final facts in nature as they present themselves completed to the observer and merely incorporate this mass of isolated data in a mountain of knowledge, but we must seek the causes which underlie these phenomena. This can not be accomplished by mere descriptions of these final products and a comparison of them, but by experimental analysis. In this, the factors which appear to us to be responsible for a definite phenomenon are isolated and allowed to react, or they are completely suppressed; that is, the conditions found in nature are artificially changed in many ways. These are the same methods which have always been applied in chemistry and physics, the so

1 A lecture delivered Dec. 14, 1910, before the Scientific Society of Berlin. Translated by permission from Himmel und Erde, Berlin, June, 1911, pp. 385–395; July, 443–457.

85360°- -SM 1912-28

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called natural sciences, which owe to this method their most wonderful advancement. It was very late, comparatively speaking, when the thought obtained that similar results might be expected in natural history, and a few decades of this opinion have led to great results.

I intend to-day to cover as far as possible, with many concrete examples, the facts which I brought before you in abstract form. We would, however, gain very little if I should attempt within the time at my disposal to touch upon all the branches of natural history to which experimentation has been applied. I therefore prefer to dwell upon only two leading questions viewed from the experimental viewpoint, and shall consider these in considerable detail. These are the old Lamarckian and Darwinian slogans "Adaptation and inheritance." In their reactions, which we wish especially to emphasize, both of them become united in a single world-stirring problem. Pure description and comparison could not give them their full meaning, they remained but empty terms, slogans, through which one was supposed to be able to explain everything, but which in truth possessed no explanation at all, and were therefore discredited, especially through the critical examination to which they were subjected by the genial August Weismann. The reaction between adaptation and inheritance, or, differently stated, the transmission of characters acquired through adaptation, the emphasizing of these characters, and the evolutionary effect produced thereby upon the parent stem of the organism, had scarcely any followers for a long time. It required and will require many tedious and prolonged experiments before that almost abandoned study will be revived in improved form, stronger and better entitled to consideration. We shall therefore, among all the problems of evolution, here confine our attention to adaptation and inheritance, but we shall constantly be in touch with that other large problem, that of reproduction. In this we shall give equal consideration to asexual reproduction by simple fission (Paramaecium) or budding (worm Aeolosoma), the unisexual reproduction by parthenogenetic eggs (lower crustaceans), or close fertilization (higher plants), and even the bisexual reproduction through the union of ovum and spermatozoa of two distinct individuals, a male and a female (higher animals).

On account of the manifold adaptations of which we shall learn, the following problems of modern biology will be touched upon, namely, Embryogenesis, or germ development; Regeneration, or repeated growth (worm Lumbriculus); Involution or Concentration (worm Aeolosoma); Transplantation, or grafting (salamander, chicken, rabbit, guinea pig); Mendelian law (midwife toad); Intravitem staining, or coloring of living tissues (moth Tineola); Immunity, or

1 The names of the organisms which furnish data for the problems of this lecture are added in parentheses to make it easier to locate them in the proper place.

resistance against bacterial or other poisons (chicken, mouse, rabbit, man).

As is well known, many of the lower plants and animals multiply by simple fission, and the resulting elements attain in course of time the form and size of the parent. Or they may multiply by having a bud developing on any part of the body, which in time assumes the form of the entire parent or animal upon which it is developed, usually separating from the parent to lead an independent existence. Multiplication of this type by fission or budding may occasionally occur in many higher animals or plants, especially so when they have been injured by mechanical separation, and each part possesses the power to regenerate the lost portion. In this asexual reproduction we realize best that the offspring resembles the parent, or in other words that the peculiarities of the parent have been transmitted to the offspring. We even accept this when the parents have acquired new characters in their individual existence, for why should the pieces possess different characters than the material from which they sprang unchanged?

Still, it is not necessarily true that newly acquired characters must appear in the progeny. Metalnikow fed Protozoa with grains of carmine and India ink. Although they devoured those indigestible particles at first, they nevertheless gradually learned to push them aside and to avoid them. But as soon as fission had rendered the organism into two daughter cells, these seemed to be ignorant of the indigestibility of the carmine or India ink, for they devoured both greedily.

Leaving out of consideration the constituents or peculiarities of those elementary building blocks of life, the so-called cells, this simple experiment, recently challenged, it is true, by Schäfer, demonstrates the following fundamental facts: That even in reproduction by simple fission germplasm, which contains the material for the next generation, must be distinguished from the purely individual somaplasm, which perishes with the single example. The bodily peculiarities, be they young or old, must be impressed upon the germplasm of the next generation in order that they may not become lost but may continue. With this, then, we state that asexual reproduction does not differ as far as their principles is concerned, from sexual reproduction. If we find transmission of acquired characters in organisms which multiply asexually, we may therefore attribute to them the same significance as in those which reproduce by the sexual methods.

Jennings found curiously misshaped examples of a Protozoan (the slipper animalcula Paramaecium, fig. 1),1 in densely populated cultures, where there was a lack of food.

Jennings transplanted one of these from the poor medium into one presenting favorable conditions and followed the progeny through 22

The figures are reproduced on plates 1 to 8.

generations. In the resulting products of this repeated division, one part was always normal while the other inherited a hornlike process. There was considerable difference in the form and size of this process, as well as in its position; at times it appeared anteriorly, then in the middle or posteriorly, so that the progeny would obtain this process from the anterior or posterior extremity of the parent. From the nineteenth generation on, the process remained on the anterior end, assuming a peculiar function; the animal used it as a gliding shoe and moved upon it on the walls and bottom of the container.

While Jennings produced this horn like process through lack of food, McClendon produced the same by means of a centrifugal or rapid whirling of the Protozoan. In the first following fission the daughter cells each possessed a horn. Later, as in Jennings's experiments, only one of the daughter cells was provided with a horn, the second one, being normal, gave rise to normal progeny only.

Another new character, on the other hand, also resulting from insufficient food in cultures, made by Jennings and McClendon, could, in spite of transfer into a rich food medium, be transmitted even by apparently normal examples, namely, the tendency to incomplete fission (fig. 1b), in which the daughter individuals remain attached, forming chains. In this manner long wormlike colonies arise, from which now and then an individual becomes separated; this, however, produces chains again, directly, or these are formed by its progeny.

Similar fusion was produced by Stole in a worm, Aeolosoma hemprichii (fig. 2), which multiplies by budding-that is, asexually, by the use of old culture water containing scant nourishment. In this case the phenomena is not transmitted to the progeny, again a reminder that asexual reproduction does not always embrace a complete transmission of all the characters, whether inherited or acquired. This worm normally has a smooth head and six pairs of bundles of setæ, on the sides of the body (1-V1). In the reproduction (fig. 2T), a new head and body with six pairs of bundles of bristles (setæ) are budded at the posterior end and later detached. But when subjected to starvation the bud fuses with the main stem into a single individual (fig. 26), which now possesses more bundles (sete) than the normal worm. If this individual be now placed in a fresh food medium and begins to bud there (b7), it will produce from the very beginning only individuals with six pairs of bundles of setæ. Likewise, the offspring are provided with the normal number of setæ, when budded from a parent which, instead of having an increased number of setæ produced by hunger, has a lesser number produced by mechanical separation (fig. 2a).

Another Polychate fresh-water worm (Lumbriculus, fig. 3), possesses like the rest of the worms, the ability to develop into new worms, from pieces cut from the body. However, according to Morgulis, not all parts of the body are able to accomplish this. If five segments are taken from the anterior region of the body (A), these will yield exactly double as many caudal segments as five segments taken from the posterior portion (B) are able to yield. After 14 days the new tails, a, b, are detached and these now produce a new head anteriorly; a1, b1, so that complete worms, although they are somewhat dwarfed, are again produced. These dwarfed worms are again robbed of their tails and must sprout another last set of tails. But one of these forms (B), produces only about half as many tail segments as the other (A). This is the result of the stronger growth power of the anterior end of the original worm, while the other is the result of the lesser growth power of the posterior segments of the original worm. The peculiar abilities of these parts have been retained in spite of the fact that the pieces were finally subjected to the same process-that is, to produce caudal segments of the head end. Differently stated, the anterior end, derived from the posterior end, has acquired the character of lesser development and transmits this to its progeny even asexually.

Recently the question of acquired characters has been diligently studied in small crustaceans. Their reproduction is a sexual one, in so far as it does not take place through budding or fission, but through the production of true germ cells. But it does not agree with our idea of orthodox sexual reproduction, since many generations may pass without the appearance of males. The reproductive products at such times are purely feminine-that is, eggs which develop without having been fertilized by a male cell, the spermatozoan. We may distinguish this form of reproduction from sexual reproduction, in the restricted sense, or bisexual reproduction, as unisexual or parthenogenetic reproduction. The investigators who have been engaged in the study of these lower crustaceans, and have in part or wholly bred them parthenogenetically from unfertilized eggs, have avoided the criticism which has often been expressed where animals were produced by the bisexual method of reproduction, namely, that the changes obtained in these animals, the product of bisexual reproduction, were not due to an adaptation to the environment, but to the crossing of races, in which certain characters, which had up to this time been hidden in the germplasm, had come to the surface. To the breeding experiments, in which the above criticism can not apply, belongs, among others of recent date, also one of the most important older works, the experiments of Schmankewitsch (1875). This deals with the effect produced upon the form of the saline crustacean (Artemia salina, fig. 4, 1), by varying the salinity

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