526 A. B. DAWSON 
GLANDS 
A. Introduction 
The large glands of the skin of Amphibia have been favorite 
subjects of study for many years. Work has been done on 
animals of all three orders. The investigations on the Gymno- 
phiona have been limited; the Urodela have been studied inten- 
sively, and, of the Anura, the families Ranidae and Bufonidae 
have received most attention. The number of kinds of glands 
has been, and still is, a disputed question. Most writers have 
described at least two kinds. These have been variously desig- 
nated as large, granular, poison, or contractile, and small, clear, 
mucous, or non-contractile, respectively. But a few investi- 
gators hold that there is only one kind of gland in the skin and 
that the various glands of other authors are but different stages 
in the development of it. . 
In several papers descriptions of mixed glands, partly of the 
mucous and partly of the granular type; have been given. There 
is much diversity of opinion regarding the significance of these 
double structures. Several workers regard the mixed gland as 
arising from a process of replacement of a granular gland by a 
mucous gland, but they are not agreed upon the ultimate fate 
of the replacing elements. Some believe that the mucous cells 
retain their original character and preduce mucus during their 
entire period of activity, while others think it highly probable 
that they assume the function of the granular cells which they 
have replaced. A second explanation of the mixed condition 
has been given by those who contend that the granular glands 
in their development always pass through a mucous stage before 
reaching their final appearance and character. According to 
this view, mixed glands would represent incomplete stages in 
the transformation of mucous glands into granular glands. _How- 
ever, the possibility of a mucous cell metamorphosing into a 
poison cell has been vigorously denied by many, who claim that 
a mucous cell is always a mucous cell and a granular cell always 
a granular cell. Hence, even among investigators believing 
in the existence of two kinds of glands, we have a diversity of 
