INTEGUMENT OF NECTURUS MACULOSUS 553 
left undisturbed no fresh mucus appears on the surface and the 
secretion already present dries, forming a thin transparent cover- 
ing. (It, however, cannot afford much protection to the epi- 
dermis, since molting follows a. prolonged drying in the air.) 
If a portion of the skin be wiped clear of mucus and a piece of 
dry filter-paper placed upon it, no secretion is discharged. If, 
however, the paper be kept moist, mucus appears beneath it in 
large quantities and soon saturates it. 
The mechanics of the discharge of the secretion from the 
mucous glands is a disputed question. Nussbaum (’82) asserts 
that when the glands of the salamander are stimulated the inner 
ends of the secreting cells are discharged. According to Drasch 
(89), secretion is a more or less continuous process and there 
is no accumulation of a great reserve to be expelled in an emer- 
gency as is the case with the larger, granular glands. He found 
that stimulation of the trigeminal nerve caused a contraction of 
the membrane about the gland, while stimulation of the sympa- 
thetic produced an increase in the volume of the mucous cells. 
Maurer (’95) thought the contraction of the perpendicular mus- 
cles of the dermis might have some effect on the glands, and 
Tonkoff (00) suggested that the elastic fibers investing the 
glands might be concerned with the expulsion of secretion. 
Those investigators who have found a muscular layer about the 
mucous glands regard the contraction of the muscle fibers as 
the direct cause of the discharge of secretion. 
In Necturus muscles are never found upon the mucous glands. 
Further, glands which are actively discharging seldom exhibit 
any evidences of contraction, but in some cases their ducts are 
very wide. No information whatever was obtained regarding 
the manner of the expulsion of the secretion, but, judging from 
the way it makes its appearance on the surface, it is forced out 
under some pressure, which must be due either to a tension 
outside of the gland or to changes of pressure within the gland 
itself. 
