170 



EDAVIN G. CONKLIN 



with the larger eggs a considerable number of oiDgonia, or of fol- 

 licle cells, fuse to make a single egg. In the very early stages of 

 the oogonia, in C. convexa, there is no marked difference between 

 the germ cells and the follicle cells ; later they differentiate and the 

 follicle cells become more numerous than the oogonia. Both 

 follicle cells and oogonia are sometimes imbedded in young 

 ooc3^tes, ,or even in the oogonia, and in such cases the size of the 

 oocytes is greater and their number fewer than in other species in 

 which such a fusion has not been observed. 



TABLE 4 

 Number, size and volume of eggs as compared with volume of adult female 



SPECIES 



C. plana 



C. fornicata. . 

 C. convexa. . . 

 C. adunca. . . . 

 Fulgur carica 



VOLUME 

 EGG 



TOTAL 



VOLUME 



EGGS 



0.001489 13.4 

 0.003156' 41.65 

 0.011494 2.53 



. 036087 

 2.13 



6.50 

 1597.5 



VOLUME 

 ADULT 9 



667 



1600 



50 



208 



R.^TIO 



VOLUME 



EGGS TO 



VOLUME 9 



1 :50 

 1 :38 

 1 :20 

 1 :32 



The adults of the several species of Crepidula are so x^ri^ble 

 in size, color and form that it is frequently difficult to distinguish 

 the species; however the egg size of each species is highly charac- 

 teristic and constant, and by this means I have been able to dis- 

 tinguish doubtful species, and in one case to show that a supposed 

 species (C. glauca Say) is only a locally modified form of C. con- 

 vexa, (Conklin, '98). I know of no other animals in which the 

 size and form of sexually mature individuals are so variable and 

 the specific egg size so constant as in the genus Crepidula. 



A similar, though less marked, size difference is seen in the male 

 sex cells of the different species of Crepidula. In table 3 the di- 

 mensions of the spermatocytes of the first and second order, the 

 spermatids, and the mature spermatozoa, both eupyrene and 

 oligopyrene, are given for C. convexa, C. plana and C. fornicata. 

 In the case of the eupyrene sperm the tail is very long, about 

 110 M in C. plana, and it is very tenuous toward the end so that 

 I have not been able to measure it with certainty ; however it is 



