THE FERTILIZATION PROCESS IN THE SNAIL. 75 



without finding definitive sperms or ova at any age up to thirty-five 

 days. Pelseneer ('96) thinks that protandry should be considered 

 general in the Euthyneura, especially in Pulmonata. Schapiro 

 ('02) believes that parthenogenesis developed first in the animal 

 kingdom, because it is more simple than hermaphroditism. On 

 the other hand Brock ('86) thinks that the sex organs of Pul- 

 monata are first laid down as female, and later become hermaphro- 

 ditic. Hoffman ('22) found that the genital apparatus is not 

 fully developed in Lima.v niaxim-us, having a length of three 

 centimeters. Certain Proso'branch gastropods have been shown 

 to be protandric, for example, Crepidula planet (Gould, '17, '19), 

 Colyptrcea sincnsis, Crepidula unguiformis and Capulus liuugaricus 

 (Giese, '15). Lams ('07) states that Anon cinpiricornin is pro- 

 tandrous. Ancel ('02) and Burescli ('12) appear to consider 

 Hcli.i- poinatia and H. arbustonun as being neither protandrous 

 nor protogynous, but hermaphroditic from the first differentiation 

 of germ-cells. Since I examined sections of several young snails 

 without finding definitive sperms or eggs at any age up to thirty- 

 five days, I think that further work will show that L. s. apprcssa 

 is neither protandrous nor protogynous, but strictly hermaphro- 

 ditic. 



VI. DEVELOPMENT AND MIGRATION OF THE GERM-CELLS. 



Both male and female germ-cells, as well as Sertoli and egg- 

 nurse-cells, appear to be able to arise simultaneously from indif- 

 ferent epithelial substance, and are commonly found developing 

 together in a single acinus in Lvinncu stagnalis apprcssa, L. coln- 

 mclla and L. palustris. Recent investigators are pretty well 

 agreed that the origin of the germ-cells in most of the gastropods, 

 especially in the Basommatophora and Stylommatophora is from 

 indifferent epithelial material. Among these may be mentioned 

 Garnalt ('88) who studied several forms of Hcli.i- ; Ruresch ('12) 

 who worked on Heli.v arbustonun; Lams ('07) on Anon cinpiri- 

 corum; and Gatenby ('18) on Heli.v aspcrsa, Testacclla halio- 

 tlodcs, Paludina, Lyinncca stagnalis and other forms of Heli.v of 

 uncertain taxonomic status. However, in his Text-fig. 5 and his 

 text, p. 601 ('17), he appears to advocate a sort of " de-differen- 

 tiation " idea for the origin of the germ- and nurse-cells in Heli.v 



