488 EIGENMANN. [Vol. V. 



No. 5. One dextral and one sinistral cell about 0.30 mm. from 

 the posterior end. 



The remaining cells are all in the posterior part of the larva, 

 and vary in number from two to eight on the right, and from 

 four to nine on the left side of the body. 



In a larva 1.1 mm. long, the anterior cells are as in Fig. 7. 

 One is in the mesoblast over the posterior part of the heart; the 

 other lies apparently between the hypoblast and brain. The 

 cells are somewhat different from those usually observed, but a 

 comparison with the sex-cells of another larva from the same 

 ovary, treated in the same way (Fig. 8), leaves no doubt of their 

 character. Further than this I have not been able to follow 

 these anterior cells, and am not able to conjecture what becomes 

 of them. 



Those of the middle of the body or of earlier stages probably 

 migrate caudad, though they may atrophy. In larvae 1.2 mm. 

 long, the sex-cells are arranged on either side in the mesoblast 

 above the anus. The two sides are not symmetrical ; there is 

 usually a group of several cells, the remainder being scattered. 

 In one larva all the cells but one are on the left ; in another the 

 majority are on the right side. The number of cells, about ten, 

 remains unchanged (Fig. 8). 



In larvae 2.5 mm. long the sex-cells have attained the posi- 

 tion figured by Balfour (PI. X., Fig. 8) for Elasmobranchs. 

 That is, they are found in the mesentery and the mesoblast ad- 

 joining it from above the anus forward. In one larva they are 

 distributed as follows, counting sections about 16 /n thick from 

 the anus forward : — 



Four median (Fig. 9). 



One median. 



One on left, two on right (Fig. 10). 



One on right. 



Two on right. 



One median. 



One on right. 



One on left. 



One median ? 



One on right ? 



There are fourteen, probably sixteen cells in this larva, and 

 the number of cells cannot have been increased much since their 



