STUDIES ON SEX IN CREPIDULA 15 



The diameters of primordial male and primordial female cells 

 group themselves about different modes. Further, the mean 

 diameter of each type is different at different periods in the life 

 of the animal. In table 1 each mean diameter is taken from 65 

 cells chosen at random and measured with an ocular micrometer. 



TABLE 1 



Mean diameter 

 {in miaa) 



Minute animals 



Primordial egg cells 11.9 



Primordial sperm cells 9.6 



Spermatogonia in lumen 8.5 



Developing males 



Primordial egg cells 12.6 



Primordial sperm cells 10.8 



Spermatogonia in lumen 8.7 



Mature males^ 



Primordial sperm cells .■ 10.2 



Spermatogonia in lumen '. 9.8 



Neuter animals- 

 Primordial egg cells 11.9 



Primordial sperm cells 10.0 



Neuter animals with large numbers of primordial egg cells 



Primordial egg cells * 11 .3 



Primordial sperm cells 9.7 



Incipient females (with oocytes going through nuclear changes) ^ 



Primordial egg cells 12.0 



1 In mature animals primordial egg cells are difficult to identify and no at- 

 tempt was made to measure them. 



2 In neuter and young female specimens there are ordinarily no spermatogonia 

 in the lumen of the gonad. 



3 Primordial sperm cells become very rare at this stage, and no attempt was 

 made to measure them. 



The follicle cells 



At the early stage of development first described above there 

 are besides the primordial male and female germ cells certain 

 other elements in the germinal layer, in the nature of follicle 



