Studies on Sex in the Hermaphrodite Mollusc Crepidula Plana. III

Resumen por el autor, Harley Nathan Gould. Universidad de Pittsburgh. Estudios sobre el sex0 en el molusco hermafrodita Crepidula plana. 111, Transmisi6n del estimulo productor de machos por el agua de mar. El molusco gaster6podo Crepidula plana pasa durante su vida por una fase de macho, una fase de transicih y una fase de hembra. La fase de macho es inestable y se presenta solamente como resultado de un estimulo susministrado por un individuo de la misma especie m&s grande que el individuo estimulado. El aislamiento completo de 10s individuos pequeiios no desarrollados sexualmente, durante largos periodos, demuestra que baj o tales condiciones no tiene lugar m&s desarrollo de 10s caracteres machos que la formaci6n de unas pocas espermatogonias. En su debido tiempo aparecen 10s caracteres de la hembra. Los individuos pequefios y no desarrollados sexualmente confinados a distancias fijas de 4 a 7 mm. de hembras grandes, impidihdose de este mod0 todo contacto, desarrollan en la mayor parte de 10s casos caracteres del macho en varios estados de madurez sexual. Bajo tales condiciones se producen menos machos y peor desarrollados que cuando 10s animales pequeiios esth m&s cerca del origen del estimulo. Los individuos grandes de Crepidula forni- cata, una especie pr6xima a Crepidula plana, no inducen desarrollo alguno sobre 10s individuos pequefios de esta liltima especie, except0 en unos cuantos casos dudosos. El estimulo que provoca el desarrollo de machos actda de tal mod0 que indica que es una substancia que sale de 10s cuerpos de 10s individuos grandes de Crepidula plana, la cual substancia es difusible en el agua de mar, per0 es muy inestable. Translation by Jose F. Nonidez Carnegir Institiition of Washington ACTHOR'S ABSTRACT OF THIS PAPER ISSUED BY THE BIBLIOGRAPHIC SERVICE, AUGUST 4 STUDIES ON SEX IN THE HERMAPHRODITE MOLLUSC CREPIDULA PLANA 111. TRANSFERENCE OF THE MALE-PRODUCING STIMULUS THROUGH SEA-WATER HARLEY N. GOULD Marine Biological Laboratory, Woods Hole, and School of Medicine, University of Pittsburgh ONE TEXT FIGURE The second paper of this series' described a number of experiments showing the instability of the male phase in the marine gastropod Crepidula plana. In common with other members of the family Calyptraeidae, C. plana passes through a sperm-producing phase during the early part of its life while it is small (up to about 15 mm. in length) followed by a transitional phase (15 to 20 mm.) and later by an egg-producing phase (20 to 40 mm.). Growth goes on with varying degrees of rapidity during life. The functional females are the largest and oldest. The species has a peculiarity in that the development and mainte- nance of the male phase requires a stimulus from the outside, which is furnished by the presence of a larger individual, usually transitional or female, in the immediate vicinity of the potential male. The animals are most commonly found in colonies adhering to the inner surface of shells inhabited by hermit crabs. The younger, smaller Crepidulas have various degrees of male development, those directly attached upon the shells of the large females as a substratum, or close beside them, being nearly all fully developed males, while those at a distance of 5 mm. or over are more likely to have only partially developed male organs; the degree of development being less in the specimens farther from the source of the stimulus, i.e., the large individuals of the colony. 1 Gould, 1917, 11. 113 114 HARLEY N. GOULD In a group in which there are no females and all the members are less than 10 or 12 mm. in length, there are seldom any adult males; the majority being, instead, sexually undeveloped (neuter) ; but often the smaller members of such a group have a rudimentary male development, evidenced by the presence of many spermatogonia in the sex gland, even some spermatogenesis and a rudimentary penis. In fact, wherever two members of the species are attached close together, however insignificant the difference in size between them, the smaller tends to begin male development. ISOLATION OF NEUTERS The adult male stage is never developed in isolated animals, nor can it be maintained after removal of a male from the colony. Wishing, however, to determine whether any partial development of male characters would take place in completely isolated specimens, the writer allowed young neuter animals to attach themselves to the inner surface of glass vials, one to each vial. These were all kept in salt-water aquaria. Selection of the specimens for the experiment was made with care from hermit shells containing only a new small C. plana. Each was examined with a lens, and only those quite devoid of rudimentary male characters were used. After isolation a few specimens were taken from time to time, examined, then fixed and sectioned for study of the gonad. At the beginning all were from 5 to 12 mm. in length, and were thus at the size when male development can easily be induced. They grew during the period cf isolation, and the last lot, taken at fifty days, were much larger. Slides were made from twenty-four specimens; two at twenty-two days’ isolation, four at twenty-four days, three at twenty-six days, five at thirty- three days, five at forty-three days, and five at fifty days. The results may be summarized as follows: External male characters: In three animals only, two twenty-four days and one at thirty-three days, there was a very small stump at the spot where the penis forms. No other external signs of the male condition appeared. STUDIES ON SEX IN CREPIDULA 115 Gonad: In three cases there were a few spermatogonia in th,e sex gland; one at twenty-two days, one at twenty-four days, and one at forty-three days. None of these corresponded with any one of the three having a rudimentary penis. In sixteen cases the gonad was inactive (containing only primordial male and female cells). The remaining five were the animals sectioned after fifty days’ isolation. They had passed from the neuter to the incipient female condition, having various stages in early growth periods of oocytes, and had grown considerably in size, being now from 14 to 23 mm. in length. A similar record was made of males removed fro% colonies and kept isolated in vials. As was shown in a former paper, all males lose their male characters after removal from the colonies. Four samples were taken from the vials after thirty-six days, four after forty-six days, four after fifty-three days, and four after sixty days. There was no resumption of spermatogenesis or redevelopment of external male organs after the degenerati0.n in any case. The only hint of any such activity was the presence of a few dividing spermatogonia in the gonad of one isolated forty-six days. It should be recalled that previous experiments demonstrated the ability of degenerate males to reassume the functional male state under stimulus from larger individuals. It is thus indicated that the gonads of isolated small specimens may produce a few spermatogonia, but proceed no further toward spermatogenesis; and the spermatogonia so formed later degenerate, as sections-show. The isolation experiment is meant to clear the way for others, i.e., to show, in cases where partial male development is induced under weak stimulus, how much of this is due to internal causes. The writer concludes that rapid sperma- togonial multiplication, formation of spermatocytes, or any later stage of spermatogenesis is an indication of an external stimulus. In previous experiments where they developed male characters under observation, the neuters were placed as closely as possible to the larger animals. Only in this way could the stimulus be clearly shown. The writer failed to find positive evidence 116 HARLEY N. GOULD of a stimulating secretion thrown into the sea-water. The ques- tion arose whether physical contact is necessary for the transference of the stimulus. STIMULUS WITHOUT CONTACT A simple apparatus (fig. 1) was devised to hold a large female Crepidula at a definite distance from a small neuter without al- lowing them to touch or to move farther apart. The female was removed from the inner surface of a hermit crab’s shell and allowed to attach herself to the concave surface of a watch crystal. The small neuter was placed on the floor of the flat-bottomed depression in a hollow-ground slide. Mosquito netting was fastened over the depression to prevent the neuter from escaping. ab d I! y I I 8 I Fig. 1 Diagram showing method of preventing contact between specimens a, large female; b, small neuter; c, depression slide; d, watch crystal. The depression slide was inverted and fastened over the watch crystal containing the large female; leaving the neuter animal, imprisoned in its cell, at a distance of from 4 to 7 mm. from the top of the female’s shell. There was no possibility of contact, yet there was little hindrance to diffusion currents in the sea- water between the two. The variation in the distance between female and neuter was due to irregularities in the curvature of the watch crystal and in depth of depression of the slide. The average distance was 6 mm. ,After various periods, samples of the originally neuter C. plana were fixed and sectioned. The results are tabulated below (table 1). Those specimens the gonads of which showed any male development beyond the mere presence of spermatogonia are marked ‘male.’ ‘Inactives’ are specimens with primordial germ cells only, or with these plus spermatogonia.

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