body, they modify in a parallel sense the representative colloids of the germinal cells, so that there would be a cumulative effect of the same general factor acting on successive generations. It is just this which has been supposed for a long time by Weismann himself and which has been designated by the name "parallel induction" (term of Detto). Weismann 10 has illustrated the fact by the celebrated example of Chrysophanus phloeas. This butterfly of very wide geographical distribution varies according to the seasons and to localities: In northern regions, the upper wings are golden red with a black border and black dots on the disk, the posterior wings blackish with a reddish submarginal band. In southern Europe there are found in the summer generation larger specimens whose two pairs of wings are almost entirely black (form eleus), with all intermediates between this form and the type. If caterpillars coming from eggs of phloeas from Naples are raised in Germany and the pupae submitted to a low temperature (10° C.), there develop butterflies a little less black than those of Naples, but much blacker than the German ones; on the contrary, pupae of German origin submitted to a high temperature (38° C.) produce butterflies which are a little less fire-red and a little blacker than the ordinary German butterflies. The hereditary character of the southern varieties, an abundance of dark pigment, is thus seen to be directed in the same way as the action of the higher temperature. We can suppose that when the species, at first northern, reached the south, the rise in temperature affected, with a like result, the formative elements of wing color, and the colloids representative of the pigment in the germinal cells. Hence the present condition. We can perhaps accept the heredity of immunity, an acquired character appearing after a germ disease; not total immunity, for we know well that this is not transmissible, but a partial immunity which is sufficient, without need of recourse to a selection of the most resistant, to explain why the inhabitants of a country where a disease commonly occurs are generally more apt to resist it than those of a country which is free from it, and that diseases which are brought into new countries cause there terrible ravages. Guyer reports that rabbits innoculated successively with typhoid vaccine, then with living typhoid germs, can transmit to their young and even to the following generation the property of agglutinating the typhoid bacilli in the dilute serum (this is, however, in contradiction with previous researches on the transmission of immunity and demands confirmation; do not the mothers remain bearers of bacilli of weakened virulence which, expelled periodically, would induce a 10 Weismann, Vorträge über Descendenztheorie. Jena, 1902, p. 306. mild infection of their young? From this fact, the latter, becoming immune in their turn, would be capable of agglutinating the typhoid bacillus and even of transferring their immunity to the second generation). Thus we begin to see, taking as a basis the experiment of Guyer and Smith, that we will be able to understand and admit the heredity of certain characters acquired through nonuse or even through use, a question which places in wide opposition the Lamarckist school and the mutationist school. It may be that an organ affected by individual nonuse (the eye, for example, of an animal living in total darkness) produces specific modifications in the body fluids, a kind of lysis, if you wish, which would affect the representative substances in the germinal cells, and would lead gradually to the hereditary atrophy of the organ. I sincerely hope that the experiments of Guyer and Smith may be done again more rigorously, in order to put an end to the discussions on the heredity of acquired characters and the intimate constitution of the hereditary patrimony. Only then will it be possible to build on a solid foundation a theory of the evolution of living beings. BREEDING HABITS, DEVELOPMENT, AND BIRTH OF THE OPOSSUM.1 By CARL HARTMAN, The University of Texas, Austin. [With 10 plates.] In the popular mind, the generation of no animal is so shrouded in mystery as that of the opossum. Throughout the country, among both whites and negroes, deeply rooted tradition has it that the opossum copulates through the nose and that the female blows the fruit of conception into the pouch. Other myths relating to details of the reproductive process in this species are current among the people. The growth of such legends need not surprise one, however, for the early birth of the embryos and the use of the pouch as an incubator certainly challenge the imagination. These phenomena attract the attention because they are unique, differing from the familiar method of rearing the young obtaining among the higher mammals, including man. Familiarity breeds contempt; the ordinary ceases to be marvelous. Thus on account of its rareness and its "different" character the opossum, our only marsupial, figures in the folklore to a prominent degree. As a matter of fact, however, in extenuation of the popular misconception alluded to, it must be said that extremely few scientific observations upon the breeding habits of this animal are recorded. For example, there seem to be only two observations on the mating habits of this species, one by Dr. Middleton Michel (1850), an American physician, and the other by Selenka (1887), the German embryologist. Likewise, the birth of a marsupial, whether American or Australian, was seldom observed; and until the writer in 1919 witnessed the actual passage of the young into the pouch the method of transfer remained an enigma even to the professional zoologist. Little published data existed, therefore, to refute myth and legend. The present paper is an attempt on the part of the writer to summarize some of his observations on the reproduction of the opossum. 1 Contribution from the Department of Zoology, The University of Texas, No. 154. His studies on the embryology of this form were begun eight or nine years ago at the instance of Prof. J. T. Patterson, following the appearance of Prof. J. P. Hill's beautiful monograph on the early stages of Dasyurus, the Australian "native cat." Notes were taken for various purposes on 685 female opossums and a complete series of several thousand eggs, embryos, and pouch young was collected. The work on so large a scale was made possible through liberal grants from the Wistar Institute of Anatomy and Biology (Philadelphia) and a $500 fund given by Mr. H. A. Wroe, of Austin, Tex., in 1920. Although the original interest centered around the development of the embryo, observations and experiments were made upon the physiology of reproduction. This paper will deal with both topics. SPECIES STUDIED Almost all of the experimental animals belonged to the species Didelphys virginiana, of which there is a gray and a black phase. These apparently occur in the proportion of about 10 to 1, respectively. The color depends entirely upon the color of the overhair, which is white in the gray phase, black in the black phase. Three albino and three cinnamon mutations have also been acquired, the latter a gift from Dr. Charles McNeil, of Sedalia, Mo., where the brown form is said to occur rather often. It would seem that the same factors underlying hair color are widespread throughout the mammalian series, including the marsupials. THE FEMALE REPRODUCTIVE ORGANS. Before going on to the main subject it is essential that the reader be familiar with the anatomy of the reproductive organs of the female opossum. The generic name Didelphys, given to the opossum by Linnaeus, has reference to a distinctive feature of marsupials, namely, the presence of two separate and distinct uteri (fig. 5, pl. 2; and pl. 3); for in the higher mammals there is but one, which may, however, be divided into the central "body" and the two "horns." Each uterus opens by a separate "os," not directly into the vagina but into a lateral vaginal canal; and the two lateral canals in turn, after describing a loop, empty separately into the median vaginal canal or vagina proper. This opens with the rectum into a short cloaca," so that there is in marsupials but one external opening ordinarily visible posteriorly, namely, the cloacal orifice. It is thus seen that in marsupials the paired arrangement of organs obtains not only for ovaries and Fallopian tubes, as in all mammals, but also involves the uteri and the lateral vaginal canals. From the standpoint of their physiological behavior the lateral vaginal canals 66 |