INTEGUMENT OF NECTURUS MACULOSUS 563 
presents several possibilities for the reader’s consideration. 1) 
The cells may not be destroyed in secretion, but rejuvenate them- 
selves from the non-metamorphosed part of the cytoplasm. In 
many cases he has found remnants of cytoplasm in the region of 
the nuclei. 2) Some cells may be destroyed in secretion and their 
loss offset by the differentiation of cells from the intercalary 
region. Mitotic figures were seldom observed and there was no 
evidence of amitosis. He suggests that the time of the year may 
have some influence on the regenerative processes in the glands. 
3) “Die Driise wird durch zapfenf6rmiges Einwachsen vom 
Oberflichenepithel aus total neugebildet.” By this he appar- 
ently means that within an exhausted gland sac new epithelial 
cells may be developed by a downgrowth from the epidermis. 
b. In Necturus. The mucous glands of Necturus never 
exhibit any evidences of the degeneration of their epithelium 
such as were found in the granular glands. The cells probably 
function for a considerable period before they are destroyed. 
New cells may be differentiated from the intercalary cells, since 
mitotic figures are occasionally found in that region. The . 
lumina of the glands are seldom free from mucus. This indicates 
that secretion is produced more or less continuously. In a few 
cases, however, mucous glands are found in which the lumen is 
almost free from secretion and the secreting epithelium appears 
to be in a somewhat exhausted condition (fig. 32). In these 
the ends of the cells next the lumen lack a limiting membrane, 
but on the sides of the cells the walls are distinct. The cyto- 
plasm containing the flattened, densely stained nuclei is confined 
to a narrow zone next the gland wall. The remaining portions 
of the glands appear empty, but the intercalary cells are highly 
developed, suggesting some activity in this region. It is difficult 
to explain satisfactorily the condition represented in figure 32, 
since cell walls are seldom found to persist in functioning glands. 
In this case the gland cells have apparently elaborated secretion 
and discharged it, leaving the cell walls intact except at the ends 
next the lumen. The general appearance of the gland, more- 
over, would lead one to believe that its time of functional activity 
is not at an end and that it is still capable of producing secretion. 
