24 BENNET M. ALLEN 
to have any high degree of accuracy, I feel that we are quite 
justified in concluding from these figures that: (1) there is a fair 
decrease in the size of the cell-body as development proceeds, 
and (2) that there is a slight increase in the size of the nucleus. 
The decrease in the size of the cell-body is probably due to 
the absorption of the yolk material with which the sex-cells are 
so richly filled during the earlier stages. No good explanation to 
account for the slight apparent increase in size of the nucleus 
presents itself. 
DISCUSSION OF RESULTS 
We can not consider this work as completed without making 
a comparison between the sex-cells and the other cells of the 
embryo. This subject will first be taken up in Amia where we 
have traced the sex-cells back to earlier stages than in Lepidosteus. 
It has already been pointed out that the sex-cells, as first seen in 
the peripheral entoderm, are to be distinguished only by the size 
and arrangement of the yolk spherules. The nuclei bear a close 
resemblance to those of surrounding cells of the same size, while 
the larger nuclei of larger cells show many points of similarity to 
them. In all except the earliest stages studied, these nuclei are 
quite rounded. The chromatin appears in the form of slender 
strands that take a peripheral position in the nucleus. There 
is invariably a plasmosome present and rarely two of them. In 
the 147 hour stage the nuclei of the sex-cells bear a resemblance 
not only to those of the neighboring cells but also to those of the 
gut entoderm. In fact, many nuclei of the mesoderm show simi- 
lar characteristics. 
After development has gone a little further, as in the 3.4 mm. 
and 4 mm. stages, the mesodermal nuclei and those of the gut 
entoderm are found to have become smaller and are more deeply 
stained than those of the sex-cells and peripheral entoderm. In 
all of these later stages, which include 5 mm., 6 mm., 9.1 mm., 11.4 
mm. and 16 mm. larvae, these differences are found to increase. 
Although the sex-cells undergo a migration from the peripheral 
entoderm into the lateral plates of mesoderm and through the 
latter to the sex-gland anlagen, they still bear a close resemblance 
