34 BENNET M. ALLEN 
garis. The discussion of his work above gives the reasons for 
my position in this matter. 
Not only does it seem probable that the sex-cells arise during 
early stages in the mesoderm of the urodeles, but this seems to be 
the case in the teleosts as well. The most recent and satisfac- 
tory support of this view is contained in the excellent paper of 
Dr. Gideon 8. Dodds upon the‘‘Segregation of the Germ-Cells 
of the Teleost, Lophius,’’ in the Journal of Morphology, 1910. 
Here again, we must urge caution in forming a sweeping general- 
ization from the facts thus far at hand. There is certainly a 
wide field for work in the study of the origin of the sex-cells of 
the vertebrates. It is a subject which should be approached in 
a spirit of broad toleration for the views of others. The sex- 
cells are cells that retain their early embryonic character after 
the somatic cells have undergone specialization. It seems, 
from a number of observations made by different authors, that 
in most forms the sex-cells first make their appearance in the 
entoderm—the germ layer whose cells appear to maintain their 
primitive embryonic characters longer than do those of the other 
germ layers. At the same time, unimpeachable evidence shows 
that this apparently logical process is not universal, and I have 
at no time claimed that it is. The sex-cells, as shown by Nuss- 
baum, Eigenmann, Beard and others, do not belong to any one 
germ layer, but are, in a sense at least, independent of the som- 
atic tissues. They are free to follow their own path in their 
travels from the place of origin to the sex-gland anlagen, where 
they finally come to rest. While this path is no doubt identi- 
cal or similar in closely allied species and in more general divi- 
sions of the vertebrates, I do not feel that we are justified in at- 
tributing a high degree of phylogenetic importance to the different 
steps in the migration paths through which they travel. 
I wish to express my indebtedness for the work of our depart- 
mental artists, Misses Hedge and Battey. I am indebted to Miss 
Hedge for the execution of diagrams 1-6 and for figs. 9, 10, 14, 
15, 21, 22, 25 and 26; and to Miss Battey for figs. f1, 12, 13, 23, 
and 24. The remaining drawings are my own. 
