20 BENNET M. ALLEN 
The first sex-cells in the somatopleure are found in the sex-gland 
anlagen a short distance (0.04 mm.) behind this point. The sex- 
cells are distributed somewhat irregularly from the cranial end 
of the hind-gut to a point 0.90 mm., caudad to this point and 
there are a few scattering sex-cells still further caudad than this. 
The coelome is apparent as a continuous cleft on either side 
of the hind-gut along the entire extent of the region occupied 
by the sex-cells. The majority of the sex-cells are to be found 
in the dorso-medial extremity of the coelome, 7.e., near the 
root of the mesentery. A few lie lateral and ventral to the 
intestine. The coelomic cleft has not as yet become wider than 
the diameter of the average sex-cell and we consequently see 
them usually bridging across it, fig. 18. In no case have they 
penetrated into the somatic mesoderm as we find them doing 
later. One sex-cell was found in the gut-entoderm, whither it 
may have migrated from the mesoderm. It is, on the other hand, 
quite possible for it to have migrated in the entoderm in the man- 
ner of sex-cell migration in the turtle. This is a point of minor 
significance and an occurrence which is at best very infrequent. 
Amia, 7 mm., total length. Up to this time, the mesentery 
has been only potentially present, the two lateral plates of meso- 
derm being in contact above the gut-entoderm. Now, however, 
we find that it has begun to elongate and become thin. This is 
naturally correlated with the increase in the extent of the coelome, 
fig. 19. Two well defined sex-cells are found in the gut-entoderm, 
0.06 mm., cranial to the opening of the hind-gut. These are to 
be interpreted in the same way as the cell in the entoderm men- 
tioned above. The first sex-cell occurring in the mesoderm is 
found 0.08 mm. caudad to the beginning of the hind-gut. The 
sex-cells are distributed through a region extending from a point 
immediately back of the opening of the hind-gut to a point 1.05 
mm. behind it, with a few scattering ones behind these. The 
total number of sex-cells is 74. 
Amia, 9.1 stage. Sex-cells first appear .18 mm. cranial to 
the opening of the hind-gut. They extend from this point to a 
point 1.59 mm. caudad to this, giving a total extent of 1.67 mm. 
The total number of sex-cells counted at this stage amounted to 
