168 



EDWIN G. CONKLIN 



TABLE 3 



Size of sex cells in different species of Crepidula 



C. CONVEXA 



C. PLANA. 



Cell 



Nucleus 



C. FORNICATA. 



Cell Nucleus Cell 



Nucleus 



Oogonia, at last divi- 

 sion 



Oocytes I, before for- 

 mation of yolk 



Oocytes I, maximum 

 yolk nucleus 



Oocytes I, maximum 

 yolk spheres 



Ootids, after fertiliza- 

 zation 



Spermatocytes I 



Spermatocytes 11... . 



Spermatid, chromatin 

 condensed 



Mature spermatozoa 

 [Head. 



Eupyrene | Middle 

 piece 



[Tail.. 



Oligopyrene (Length 

 '• \ Width. 



27 

 57 



280 

 9 

 8 



24 



30 

 110 

 66 

 1.5 



15 



28 

 27 

 36 



7 

 6 



12 

 36 



142 

 8 

 7 



15 



30 



54 

 2 



6 

 20 



6 

 15 



6 

 5 



15 

 42 



12 

 24 

 12 

 12 



182 



12 



30 



54 

 2 



smaller eggs producing free-swimming larvae while the larger eggs 

 give rise to larvae which undergo metamorphosis within the egg 

 capsules and escape only when the adult form has been reached. 

 The larger eggs have a much larger quantity of yolk than the 

 smaller ones, but they also have a larger quantity of cytoplasm 

 and larger nuclei; even in the oogonial stages, before any yolk is 

 formed, these cells are much larger in C. convexa than in C. plana; 

 indeed these oogonia differ as much in size as do the mature eggs. 

 It would be a great mistake to suppose that the larger eggs differ 

 from the smaller ones merely in the quantity of yolk which they 

 contain, as is usually assumed. Such a marked and constant 

 difference in the size of egg cells, where other types of cells are so 

 uniform, is significant. There is some evidence that in the species 



