BODY SIZE AND CELL SIZE 



183 



and insignificant, and these results, which were briefly reported 

 in both of my former papers on this subject ('96, '98), show that 

 differences in the body size of different individuals are due to the 

 number of cells present rather than to the size of individual cells. 

 To quote again from one of the papers referred to ('98, p. 438) : 



It is an almost impossible task to count the number of cells present 

 even in a very small organ. I have, however, been able to count the 

 number of cells present in cross sections of the rectum, and while the 

 size of the cells here, as everywhere, is the same in the large as in the 

 small individuals the number of cells is greater in the former than in the 

 latter. 



Of all the cells of the body, the ova are most easil^^ enumerated ; they 

 are laid in capsules which can be easily counted, and each of which con- 

 tains a nearly constant number of eggs. Oft repeated observation shows 

 that without exception the fertilized, but unsegmented, eggs of the 

 dwarfs are of exactly the same size as those of the giants, but are very 

 much fewer in number; e.g. table 8 shows the averages obtained from 

 a larger number of observations. 



It is notable that the number of capsules formed is nearly the same in 

 the two varieties, though there is a great difference in the number of 

 eggs inclosed in each capsule. 



In Crepidula, therefore, the cell size is fairly constant, and variations 

 in the size of the body are due to variations in the number of cells present. 

 . . . . Whatever the cause of the dwarfed form may be, it will be 

 noted that in Crepidula it operates by stopping growth and cell division. 



3. CELL SIZE AND BODY SIZE IN MALES AND FEMALES OF 



C. PLANA 



Marked as is the environmental dimorphism in C. plana, the sexual 

 dimorphism is even greater (table 1), the average female being almost 

 fifteen times as large as the average male. In all species of Crepidula 

 the males are smaller than the females, though the chfference in size is 

 greatest in C. plana. 



TABLE 8 

 Size and number of eggs laid by typical and dwarfed individuals of Crepidula plana 



C. plana (type). . 

 C. plana (dwarf). 



DIAMETER OF 

 EGG 



1.36* 

 136* 



NUMBER OF 

 CAPSULES 



51 



48 



EGGS IN- 

 CAPSULES 



176 

 64 



TOTAL NUMBER 

 OF EGGS 



9,000 



3,070 



*More recent measurements, made with another scale and other lenses, show 

 the eggs to be about 142 ju in diameter before the first cleavage, as given elsewhere 

 in this paper. 



JOURNAL OF MORPHOLOGY, VOL. 23, NO. 1 



