486 EIGENMANN. [Vol. V. 



plasm immediately surrounding it. In an embryo cut in a sag- 

 ittal direction there are two cells having the character of the 

 sex-cells in the front part of the head (Fig. 5), probably closely 

 connected with the rudiments of the ear ( ?). One lies in the 

 mesoblast some distance behind (Fig. 5, s.c. ?), and a group of 

 them lies just in front of the first protovertebra (Fig. 6), and two 

 lie at the posterior extremity of the embryo ; but about the char- 

 acter of those two cells I am not positive. 



The cells in this embryo measure 13-18 /-i ; the nucleus, 4-6 /x. 

 They are distributed in detail as follows: sections 14-18 being 

 on the left of the median line of the body, sections 24-30 to 

 the right of it; section 15 has one in the mesoblast of the head, 

 three cells in front of the first protovertebra; section 16 has 

 four in the same region, just in front of the first protovertebra ; 

 section 17 has one in the same region, and one larger, with more 

 regular outlines further forward; section 18 has one in the 

 region of the ear, and two in the posterior end of the embryo ; 

 section 24 has one in the region of the ear, and two in the 

 mesoblast of the head just before the first protovertebra; sec- 

 tion 25 (Fig. 6) has five in the mesoblast of the head ; section 

 30 has a dark cell on the edge of the mesoblast well forward, 

 the nature of which is open to doubt. The great majority of 

 the sex-cells in this embryo have collected in the mesoblast 

 of the head just in front of the first protovertebra ; only two 

 out of all these cells are as yet posterior to the head, and the 

 character of these two cells is doubtful. 



In another embryo of this stage (cut transversely), in which 

 there are seven in the left and eight in the right side of the 

 body, the cells are all found in the cephalic region, or at least 

 very near it. 



In still another, cut in a plane slightly inclined to the hori- 

 zontal, approximately the same conditions are found. 



In several places, as in Fig. 6, the cells are grouped together. 



In a larva just hatched, the longest diameter of which, 

 measuring in a straight line, is 0.45 mm., there are ten sex- 

 cells. In this embryo about nine protovertebrse have been 

 formed. Most of the sex-cells are large, the largest having a 

 diameter of 23 fi, with a nucleus of 8 \x. The smallest cell 

 measures but 1 1 /i in diameter. The distribution of these cells 

 has become markedly changed from the conditions obtaining in 



