26 BENNET M. ALLEN 
There are two ways of viewing the similarity that the sex- 
cells of Amia and Lepidosteus bear to these cells of the peripheral 
entoderm. The well defined cells of the peripheral entoderm 
might be interpreted as sex-cells that have failed to migrate into. 
the lateral plates of mesoderm. It would then remain to give an 
explanation of the resemblance that the nuclei of these cells bear 
to the nuclei of the vitelline entoderm and to account for the 
intermediate types of nuclei by which they grade into one another. 
The other view of this problem is to consider sex-cells, periph- 
eral entoderm cells, and vitelline entoderm cells as slightly differ- 
entiated blastomeres, dating from an early stage of development, 
and to consider the similarity that they bear to the cells of 
the peripheral entoderm as due to the fact that they too have 
remained in a relatively slightly differentiated condition. This 
view seems the more probable of the two. It is by no means a 
new one, having been advanced by Nussbaum in 1880. 
It would be rash in the extreme to claim that the sex-cells 
might not differin some essential chromosomal characters from 
the cells of the peripheral entoderm which they so closely resemble, 
and yet careful study has failed as yet to show any real differences. 
While such differences may exist, these cells all have much in 
common with one another. 
In a recent paper by A. P. Dustin (07), this author gives a new 
view of the origin and movements of the sex-cells of Triton alpes- 
tris, Rana fusca and Bufo vulgaris. Since his view is so greatly 
at variance with my own, it will be necessary to review this work 
in some detail. He begins with an account of the sex-cells of 
Triton, and stress is laid upon this form, the author showing a 
strong tendency to bring his studies upon Rana and Bufo into 
line with his work upon Triton. 
He first recognizes the anlage of the sex-cells in the medial 
portions of the lateral plates of mesoderm in the 3 mm. larva of 
Triton. They occur only in the caudal half of the body and 
involve only those parts of the lateral plates of mesoderm lying 
medial to the Wolffian ducts. In the early stages these cells are - 
filled with large yolk spherules and do not greatly differ from the 
mesodermal cells that surround them. At a later period the sex- 
