184 EDWIN G. CONKLIN 



In the case of the males, as in that of the dwarfs, the smaller size of the 

 body is due to the smaller number of cells present rather than to the 

 smaller size of the cells. Careful measurements of the cells of the intes- 

 tine, stomach, liver, kidney, muscles of foot, epithelium of gill chamber, 

 epithelium of gill filaments, etc. show that the cell size remains the same 

 in the male as in the female (table 7). Whatever the ultimate cause of 

 the smaller size of the males may be, it operates in this case as in that of 

 the dwarfs, by causing a cessation of growth, and cell division. 



It seems probable from the observations of Orton ('10) as well 

 as of myself (Conklin '98) that the small males of the genus Cre- 

 pidula may sometimes grow into the larger females, and that we 

 have here a case of protandric hermaphroditism. If so the small- 

 ness of body size and cell number in the males of this genus may 

 be considered to be youthful characteristics. 



I have found no evidence that the difference in the size of adult 

 males and females is associated with differences in the size of the 

 eggs as is the case in rotifers, phylloxerans, and Dinophilus, and 

 if protandric hermaphroditism occurs in this genus, such dimor- 

 phism of the egg would not be expected. 



4. CONCLUSIONS 



In the genus Crepidula differences in body size may be very 

 great; the volume of the average male of C. fornicata is one hun- 

 dred and twenty-five times that of the average male of C. con- 

 vexa; and the volume of the average female of C. fornicata is thirty- 

 two times that of the average female of C. convexa. Within the 

 single species, C. plana, the volume of the average female is about 

 fifteen times that of the average male and about thirteen times 

 that of the dwarf female of the same species. 



In spite of these great differences in body size, the size of tissue 

 cells is approximately the same in all species examined, and in all 

 individuals of both sexes and of very different sizes. In the main 

 differences in body size are due to differences in the number of 

 cells persent, and not to variations in the size of individual cells. 

 Ganglion cells and muscle cells form the principal exception to this 

 rule. 



These results agree with most of the work which has been done 

 on cell size in relation to body size, and particularly with the re- 



