28 BENNET M. ALLEN 
vitellines, le noyau, souvent réfoulé 4 la périphérie de la cellule, pré- 
sente 4 sa surface une série d’encoches lui donnant un aspect hérissé 
(p. 476). 
He finds the number of sex-cells in Rana to increase gradually, 
from 75 in the 8 mm. stage to 90 in the 15 mm. stage, at which 
time sex-cells begin to be formed by the transformation of ordi- 
nary peritoneal cells. Simultaneously there is a degeneration 
of sex-cells which is overbalanced by this process of transforma- 
tion. 
In criticism of the above views I wish, first of all, to admit the 
possibility that Dustin may be perfectly correct in his account 
of the origin of the first line of sex-cells from the lateral plates 
of mesoderm in Triton. His account of this feature is circum- 
stantial and rather convincing. His account of a transformation 
of peritoneal cells into sex-cells during later stages is by no 
means so easy of acceptation. His figures to demonstrate this 
are not convincing. 
His counts of sex-cells are not given in any circumstantial 
detail and there is no indication as to whether the number of sex- 
cells recorded for any given stage is the result of a count of the 
sex-cells in one specimen or in several. One can not be blamed 
for being skeptical of the value of such counts if made upon but 
one specimen of each stage, when so few stages are chosen to 
demonstrate general processes of degeneration and new formation. 
Such a process can only be established by a count of the sex- 
cells of numerous specimens. 
I wish to express my complete disbelief in the first appearance 
of the sex-cells in the lateral plates of mesoderm of Rana and 
Bufo in the manner described by Dustin. In my paper upon 
‘“‘An Important Period in the History of the Sex-Cells of Rana 
pipiens” (’07) I showed that the sex-cells migrate upward from the 
median dorsal portion of the gut entoderm at the time when the 
two lateral plates are pushing together to the median line in 
the process of forming the mesentery. Attention was called to 
the resemblance that this process bears to an actual pinching 
off of the mass of sex-cells by the inner margins of the plates of 
