ys BENNET M. ALLEN 
sometimes used for the later stages, but showed no superiority 
over the haem-alum. In the earlier stages of development it 
could not be used at all, owing to the deep stain that it gives the 
yolk material. 
With the abundance of material and the amount of time given 
to the work, it was possible to make a careful study of a large 
series of stages, much larger than it has been found necessary 
to use in the preparation of this paper. 
It is not necessary to enter into a detailed account of the 
earlier work upon the origin of the sex-cells, because that has 
already been done in earlier writings. Since the author’s articles 
on the sex-cells of Chrysemys and of Rana, some important papers 
have made their appearance, which, with one exception, bear 
out in a most gratifying manner the conclusions expressed by the 
writer in the two papers mentioned above and in somewhat less 
confident manner in the earlier writings of Wheeler, Woods and 
Beard. 
These papers will be discussed in the light of the facts set 
forth in this paper in the last part of this article, since they are 
to be considered in a more or less controversial manner. 
OBSERVATIONS UPON LEPIDOSTEUS OSSEUS 
Lepidosteus, 4 mm. total length. Cells which appear to be sex- 
cells lie in the ventral portion of the single layered gut entoderm. 
They can be but dimly distinguished from the other cells of the 
entoderm among which they lie. They have a more spherical 
shape than the other entoderm cells, never being flattened as the 
neighboring cells frequently are. Another difference lies in the 
fact that the sex-cells contain more and decidedly larger yolk 
spherules than do the adjoining entoderm cells. Unfortunately 
these differences are masked by the large quantities of yolk 
found in the entoderm at this stage. This is true to so great an 
extent than one can not be certain at this stage as to the identity 
of the cells in question. At this period the hind gut has a much 
greater diameter than it has at later stages. At a point one- 
quarter the distance from its cranial to its caudal end it has a 
