562 A. B. DAWSON 
be remembered that on one side of the gland sac a new undiffer- 
entiated granular epithelium was found resting on a completely 
developed muscular layer. This, as already suggested, is best 
explained by assuming that the granular half of the gland had 
functioned, and that, the old epithelium having been destroyed, 
a new replacing epithelium had moved down. ‘The correlation 
between the development of a muscular wall and the presence 
of granular cells, contrasted with the lack of muscle fibers on 
the mucous portion of the gland, strengthens the conclusion that 
mucous glands never possess a muscular layer. 
At no time in their development do the replacing cells give 
any evidence of being of mucous character and they never are 
arranged to form a small tubular sac within an unemptied 
granular gland, as in Triton. The regenerative process is never 
initiated till the fully elaborated granular secretion has been 
expelled and the remnants of the old gland cells are being removed. 
Regeneration of the granular glands in Necturus, therefore, is 
unlike that described for any other Amphibian, and also furnishes 
- additional proof that the granular and mucous types of glands 
are entirely separate and distinct from each other in develop- 
ment as well as in histological structure. 
2. Of mucous glands. a. In other Amphibia. Few authors 
have given any attention to the regeneration of the mucous 
glands. They have generally regarded them as producing secre- 
tion more or less continuously and have usually dismissed the 
subject by assuming that the individual cells function for a 
considerable time and, eventually becoming exhausted, are 
replaced, probably through mitosis. Talke (00), who has 
investigated rather carefully the processes of regeneration in the 
glands of many Amphibia, concludes that the supply of mucous 
cells is in all cases maintained by indirect division. Esterly 
(04, p. 243), in referring to the mucous glands, says: ‘It seems 
correct to say that the processes there are like those in milk 
glands where parts of the cells bodies are thrown off as secretion, 
while the remaining portions in time repeat the same processes 
of secretion.” 
Arnold (’05), in his discussion of regeneration of the mucous 
glands, does not come to any definite conclusions, but merely 
