SEX-CELLS OF AMIA AND LEPIDOSTEUS ial 
A glance at table 2 shows that there is a general tendency to a 
reduction in the average size of the cell body in the later stages. 
This may be due to the absorption of the contained yolk material. 
There is no marked change in the size of the nucleus. 
TABLE 2 
Dimensions of sex-cells of Lepidosteus 
CELL BODY 
Stage Nucleus LARGEST SMALLEST AVERAGE 
mm. 
8.6 | 6.04 | 15.10 | 12.08 13.74 
9.3 6.04 | 18.12 12.08 | 14.95 
10.7 6.04 1520 11.32 | 13,59) « 
14.0 | 5.81 12.08 9.06 | 10.27 
17.0 | 6.04 13.59 | 9.06 | 163 
24.0 | 5.81 9.06 | a5 | 8.65 
110.0 | 6.53 14.50 9.22 12.40 
AMIA CALVA 
Amia 4 mm., total length. In the text figure A is shown a 
transverse section of an Amia larva of this stage. It will serve 
as a starting point from which we shall proceed to consider still 
earlier stages in tracing out the earliest phases in the origin and 
migration of the sex-cells. The section shown is taken ‘just 
anterior to the hind gut, the gut entoderm being clearly marked 
by its greater thickness and dorsal curvature. The cavity of the 
intestine at this point opens into the large sub-germinal cavity. 
The extra embryonic portions of the entoderm, 7.e., those which 
do not form part of the anlagen of the alimentary tract and its 
appendages can logically be divided into four different regions: 
(1) The roof of the sub-germinal cavity which is distinguishable 
from the gut entoderm, as indicated; (2) The layer forming the 
floor of the sub-germinal cavity; (8) The peripheral layer of 
entoderm lateral to the sub-germinal cavity (peripheral entoderm) ; 
(4) The central yolk mass, or vitellus (vitelline entoderm). In 
the first three of these regions the cells are arranged in a single 
layer. They are characterized by the fact that the yolk spherules 
of the component cells are distinctly smaller than are those of 
