BODY SIZE AND CELL SIZE 167 



Although the body size differs greatly in different species of 

 Crepidula, the volume of an adult male of C. fornicata being 

 one hundred and twenty-five times that of the male of C. convexa, 

 and the volume of an adult female of C. fornicata being thirty- 

 two times that of the female of C. convexa, the size of the tissue 

 cells is practically the same in all of these species. Of course it 

 follows that the number of cells is much greater in the larger sized 

 species than in the smaller sized ones. 



c. Sex cells. In one type of cell, the sex cells, there is a constant 

 and considerable difference in size between the different species. 

 In all stages of the development of the ova, from the last genera- 

 tion of oogonia to the fertilized egg, these cells differ markedly 

 in size in the different species. In C. convexa, C. fornicata, and 

 C. plana the diameters of the oogonia at the time when they are 

 preparing for their last division are 27 ix, 16 fx and 12 jjl respec- 

 tively. Similarly the first generation of oocytes, before the for- 

 mation of yolk begins, measure 57 /j., 42 ^ and 36 ,u respectively 

 in these three species. These differences in the diameters of the 

 oocytes are associated with corresponding differences in the sizes 

 of their nuclei, yolk nuclei and yolk spherules, as is shown in 

 table 3. 



There are also differences in the manner of yolk formation in 

 these three species; in C. plana and C. fornicata the yolk granules 

 appear to be formed pretty uniformly throughout the protoplasm 

 of the egg; in C. convexa the yolk is formed at the base of the 

 cell, where it is attached to the jovarian wall, while the portion 

 of the oocyte next the lumen of the follicle is a cap of protoplasm 

 which for a long time remains free from yolk. 



Finally the dimensions of the fertilized but unsegmented eggs 

 of four species of Crepidula and one species of Fulgur, together 

 with the average number of eggs laid by each mature female, 

 and the total volume of these eggs as compared with the body 

 volume, is given in table 4. There is here no constant relation 

 between the size of the individual egg and the volume of the adult, 

 though in general the species of Crepidula of smaller body size 

 produce the larger eggs (v. Conklin, '97). On the other hand the 

 size of the egg is correlated with its mode of development, the 



JOURNAL OF MORPHOLOGY, VOL. 23, NO. 1 



