Sy BENNET M. ALLEN 
split to form the coelome, the sex-cells adhere to the somatic 
layer at a point near the root of the developing mesentery—the 
sex-gland anlage. They later sink into the peritoneum of this 
region, which afterwards proliferates to form a long ridge—the 
sex-gland. Very few sex-cells fall by the wayside in this migra- 
tion, practically all reaching the sex-glands. 
3. In Lepidosteus the sex-cells, first seen in the ventral and 
lateral portions of the gut-entoderm, migrate to occupy a position 
in the dorsal portion of it, from which they pass dorsally into 
the loose mesenchyme that forms the substance of the developing 
mesentery. As the mesentery becomes more narrow and com- 
pact, owing to the increase in size of the body cavity, the sex- 
cells migrate to its dorsal portion and laterally to the sex-gland 
anlagen. Roughly speaking, one-half of the total number of 
sex-cells reach the sex-gland anlagen, the remainder being dis- 
tributed between the intestinal entoderm, the mesodermal layers 
of the intestine, the mesentery and the tissues at and dorsal to 
the root of the intestine. 
4. The number of the sex-cells in Amia and Lepidosteus is a 
matter of individual variation for those periods of development 
during which they do not undergo division. The average number 
in Amia, after the period when the migration from the entoderm 
to the mesoderm has been completed, up to the latest stage in 
which counts were made, was found to be 75. In Lepidosteus it 
was 765, an average of 636 of these occurring in the mesoderm. 
5. There is a close resemblance between the nuclei of the sex- 
cells and of the yolk cells. This is especially true of certain 
cells of the peripheral entoderm, although these grade by gradual 
transition forms into the large nuclei of the vitelline entoderm. 
This is probably due to the fact that both types of ¢ells have 
undergone but little differentiation in the course of development. 
POSTSCRIPT 
A few days before proof of this article came to hand, I received, 
through the courtesy of the author, a reprint of an article by A. P. 
Dustin, entitled, ‘‘L’Origine et Evolution des Gonocytes chez 
