INTEGUMENT OF NECTURUS MACULOSUS 559 
epithelium. The frequency of mitosis in the old gland epithelium, 
coupled with entire absence of gland sacs from at least one-half 
- of the large glands, has led him to conclude that regeneration by 
replacement was rather an exceptional occurrence. 
In Plethodon, Esterly (04) found that the method of renewal 
of the worn-out glands was the same as that described by Nicoglu 
(93), Heidenhain (93a), and Vollmer (’93). He, however, 
obtained no evidence to show the source of the replacing glands, 
and, according to him, the bud is always mucous in character. 
Although Esterly has never observed transitional stages between 
the mucous bud and the poison gland, he believes the former 
replaces and assumes the function of the latter. For the frog, 
Arnold (’05) could not come to any definite conclusion regarding 
regeneration. In one case he found a small epithelial sac just 
within the neck of the gland and in several other places he noted 
small sacs with both muscle and secreting cells lying along the 
gland necks, but on account of their small size he was unable 
positively to demonstrate their relation to the old gland. 
Nirenstein (08) worked on Salamandra maculosa and Triton. 
He criticises the views of Heidenhain (93a), Nicoglu (’93), 
Vollmer (93), and Esterly (04) regarding the significance of 
the gland sacs. According to him, the gland sacs within the 
old glands are not concerned in regeneration, but represent stages 
in the development of the large gland. He claims further that 
sacs never appear of other than the mucous type and states 
that they represent portions of mucous epithelium which have 
not yet metamorphosed into poison cells. 
Regarding the fate of the discharged granular glands, Niren- 
stein was in doubt. In many eases the old secreting cells gave 
unmistakable evidence of degeneration. The lumina of the 
glands were filled with numerous wandering cells, small 
mononuclear leucocytes, large polymorphonuclear leucocytes, 
large eosinophilous leucocytes, and pigmented wandering cells. 
Besides degenerative changes, regenerative activities are also 
observed, the latter occurring in the muscle cells of the glands. 
Rapid mitotic divisions took place in this layer and locally . 
within many glands several layers of cells were produced. Fur- 
