INTEGUMENT OF NECTURUS MACULOSUS 549 
resembles that often found in ordinary epidermal cells, and does 
not seem to be identical with the granular stage described by 
other writers. From the first the secretion presents the same 
appearance and gives the same staining reactions as do the con- 
tents of the mature mucous cells. In the early stages of its 
formation the mucin gathers near the free surface of the cells, 
and a mass of secretion is thus produced which is sharply marked 
off from the underlying cytoplasm. As more secretion is pro- 
duced the nuclei are gradually forced to the bases of the cells, 
where they lie imbedded in a small amount of unchanged cyto- 
plasm. The nuclei usually become much smaller and lose their 
spherical or ellipsoidal form. The chromatin network also 
vanishes and the nuclei appear as densely stained homogeneous 
masses. In late stages, while the cell walls are still intact, the 
entire mucous cell exhibits a vesicular structure, little or no 
cytoplasm can be distinguished, and the nucleus is found in 
one corner of the cell closely pressed against the gland wall 
(fig. 28). Later, the cell wall is ruptured and the secretion 
escapes. 
4. Physiology. a. Of the granular gland. When Necturus is 
resting quietly in the aquarium, no secretion can be observed on 
the surface of the body, although the animal always feels slimy. 
A discharge of mucus can be obtained very readily by handling 
or any slight mechanical stimulation, but the granular secretion 
is expelled only in response to some violent stimulus, either 
mechanical, chemical, or electrical. 
I have been unable to learn what constitutes a proper stimulus, 
under natural conditions, for the discharge of the granular glands. 
The results of artificial stimuli differ. Electricity applied to a 
limited area of the skin causes an expulsion of the secretion in 
that region alone. Severe mechanical stimuli, sufficient to cause 
writhing movements, usually induced a general discharge from 
the granular glands. Killing with chloroform in every instance 
produced a general expulsion of both mucus and granular secre- 
tion. Animals which were wrapped loosely in towels and placed 
in the water usually discharged large quantities of both kinds 
of secretion while they were endeavoring to free themselves from 
confinement. 
