10 F, L. LANDACRE 
stage of this series was fixed immediately after collection and the 
medullary folds appear in stage 6. This series, judged by the 
size of the egg clusters and character of development, is evidently 
Plethodon glutinosus. 
The second series is older and consists of thirty-two stages 
taken from four egg clusters reared at room temperature and 
fixed at intervals of about five hours. The total period covered 
by this series is about eight days. The youngest stage of this 
series corresponds closely to no. 32 of series I. The larvae were 
reared and identified as Plethodon glutinosus. These larvae 
hatched in the twenty-fourth stage, so that combining series 
I and II there are fifty-six stages taken previous to hatching. 
The third series (series III) consists of fifty-one stages taken 
from five egg clusters reared at room temperature and fixed at 
four-hour intervals. The total period covered is again about eight 
days. ‘The first stage of series III corresponds closely to no. 10 
of series I and the twenty-third stage of series III corresponds 
to no. 1 of series II. ‘The larvae of this series were reared up to 
metamorphosis, but escaped before an identification could be 
made. Seventeen stages of this series only were cut. 
Including duplicates, there are 292 slides in all. All stages 
were cut transversely, and critical stages were cut in the sagittal 
and coronal planes also. The material was fixed in Zenker and 
stained in Delafield’s haematoxylin and counterstained in orange 
G. The younger stages were covered with a film of celloidin. to 
prevent the loss of yolk-laden cells which are likely to become 
detached. ‘The closeness of the series and their sequence are 
particularly important in the discussion of the problem involved 
in this paper. Where a series is taken from more than one 
cluster of eggs, care was used to insure that the series would be 
continuous by having the eggs taken from the two lots overlap 
in time. ) 
