SEX-CELLS OF AMIA AND LEPIDOSTEUS 17 
in the mesoderm of seven specimens of the 147 hour stage. These 
specimens were all taken from the same nest and kept in the 
same dish, so there can be but very slight difference in their ages, 
due, if it exists, to the small difference in the time at which the 
eggs were laid. It will be seen that the total number of sex- 
cells in the entoderm in these spectmens varies from 22 to 76. 
The latter number is not only greater than that observed in the 
3 mm., 155 hour stage, but almost equals that counted in many 
specimens of older stages after migration has been completed, 
as, for instance, the 11.4 mm. and 15 mm. stages (see table). 
In this stage clearly defined sex-cells can be seen in the peripheral 
entoderm just below the lateral plates of mesoderm, figs. 16 and 
17. These cells are distinguishable from the other entoderm 
cells among which they lie, by the greater size of their contained 
yolk granules as contrasted with the small size of the yolk granules 
in the other cells that make up this layer. The difference is 
further marked by the more rounded form of the sex-cells. Com- 
parison of these sex-cells in the peripheral entoderm shows them 
to be identical with other more clearly defined sex-cells in the 
mesoderm. Of this identity there can be no question, and it is 
equally clear, from a study of later stages, that these cells, having 
once migrated into the lateral plates of mesoderm, pass unaltered 
along the latter to come finally to rest in the sex-gland anlagen. 
There can be no doubt about the origin of the sex-cells from the 
entoderm. A number of cases were observed in which the sex- 
cells were actually in process of passing from the peripheral ento- 
derm into the lateral plates of mesoderm. 
At this stage, sex-cells have a wide distribution in the periph- 
eral entoderm, being scattered through a region extending 
from a point opposite to the region where the blood cells originated 
to the junction of the peripheral, sub-germinal and roof entoderm. 
In three specimens of the 137 hour stage, conditions are quite 
similar to the foregoing. In these embryos the number of sex- 
cells ranged from 11 to 29. It will be seen that the maximum 
number of sex-cells counted in this stage is greater than the 
minimum number of the 147 hour stage, although in all three of 
these 137 hour embryos, the caudal end of the embryo, that part 
JOURNAL OF MORPHOLOGY, VOL, 22, NO. 1 
