GERM CELLS OF ANURANS 281 
The first view can be traced back to Nussbaum ('80) who 
claimed that germ cells are not derived from the soma, but are 
early differentiated segmentation products which take no part in 
body formation and retain their primitive embryonic character. 
Many facts supporting this view have come to light through 
study of the origin of the germ cells in almost all classes of verte- 
brates. There can be no question that in most vertebrates the 
sex cells are early set aside during development, and later 
migrate into the germ ridges. In the embryo frog this process is 
readily traced through every stage; the same is true of other forms, 
also, as, for instance, certain ganoids, reptiles, and birds. 
The second or mesodermal view, viz., that the germ cells arise 
from an original sexually indifferent germinal epithelium origi- 
nated with Waldeyer ('70) and has been held by a great many 
observers to be the true method of germ-cell origin. Oddly 
enough, practically every animal claimed by the 'entodermists' 
as illustrating their view has also been claimed by the 'mesoder- 
mists' as illustrating their theory. For instance, take the Am- 
phibia : Allen, King, and Witschi hold the view that the primordial 
germ cells arise from the entoderm and give rise to the definitive 
sex cells; on the other hand, Semon, Bouin, Dustin, Kuschake- 
witsch, Champy, and Gatenby are all equally certain that the 
definitive sex cells of the amphibia arise from the germinal epi- 
thelium. These views are diametrically opposed, consequently 
both cannot be either entirely true or entirely false, and the 
problem is to point out if possible the source of confusion. To 
take the case of the frog again, in this form the primordial sex 
cells unquestionably arise from the entoderm. There is abso- 
lutely no indications of germ cells arising from the germinal epi- 
thehum in early larval stages. The two types of cell in the gonad, 
mesothelial and sexual, are entirely distinct and it would be 
difficult to confuse them. All increase in germ cell number is 
by mitotic division of preexisting, difTerentiated primordial germ 
cells. This state of afTairs persists until the tadpole is about 45 
to GO mm. total length. Thus far it is obvious that the evidence 
derived from the frog is decidedly in favor of the 'entodermists.' 
However, practically all of the germ cells derived from the ento- 
