H 



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 (neu- 

 ter) ; but often the smaller members of such a group have a rudi- 

 mentary 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 develop- 

 ment 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 speci- 

 mens for the experiment was made with care from hermit shells 

 containing only a^ew small C. plana. Each was examined with 

 a lens, and only those quite devoid of rudimentary male charac- 

 ters 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 of 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 exter- 

 nal signs of the male condition appeared. 



