INTEGUMENT OF NECTURUS MACULOSUS 489 
INTRODUCTION 
A. Plan and purpose 
The skin and especially the large skin glands of Amphibia 
have been the subjects of much study and discussion since 
Ascherson’s investigations on the frog in 1840. <A survey of 
the literature on these subjects since that date reveals a funda- 
mental ground-plan for the integument of all Amphibia. In 
many groups, however, peculiarities of structure and function 
of great interest appear, doubtless called forth by changes in 
habitat and manner of living. The failure of many investigators 
to realize that actual differences might exist has led to much 
unnecessary controversy. Still it is obvious that, even in cases 
where identical structures have been described, differences of 
interpretation are bound to occur. In this paper there will be 
no attempt to extend the writer’s interpretations of conditions 
found in Necturus to the whole class of Amphibia. Rather, an 
effort will be made to point out wherein Necturus resembles the 
other members of this class and wherein it is specifically different. 
This particular study was undertaken originally to determine 
the relation, if any, between the two apparently distinct types 
of dermal glands in the Necturus skin. During the early stages 
of the work other interesting problems relating to epidermal 
and dermal elements presented themselves, and it was decided 
to extend the work to include the entire integument of the animal. 
The other interesting problems of the epidermis are con- 
nected chiefly with the so-called cuticular margin, the unicellular 
glands, and pigmentation. Also the structure of the dermis, 
its relation to the epidermis, the distribution of elastic tissue, 
dermal pigmentation, and changes in coloration are described. 
As already intimated, the major part of the work is devoted to 
the large glands, of epidermal origin, imbedded in the dermis. 
In these the principal questions concern, 1) the identity of the 
granular and mucous types; 2) the nature of the secreting epi- 
thelium; 3) the elaboration and expulsion of the secretion, and, 
4) the subsequent fate of the glands. Some attention is also 
paid to the innervation of the various elements. 
