488 TRANSACTIONS OF THE CANADIAN INSTITUTE. [Vou. VIII. 
would compensate for the lack of lungs. The conclusions reached were 
not uniform, some investigators accepting both skin and bucco-pharynx 
with more or less of the cesophagus as sharing with something like equal 
importance in the respiration, others concluding that the skin is no more 
efficient in respiration in lungless salamanders than in those with lungs. 
Some examinations of Plethodon along these lines was in progress but 
ceased when the paper of Seelye (’06) on the Circulatory System of Des- 
mognathus came to hand for the points already dealt with showed that the 
conditions in Plethodon would be but a repetition of those in Desmogna- 
thus: and would lead to the same conclusion, namely that as an organ of 
respiration the skin is much more important in lungless than in lunged 
salamanders. The same paper also gives a sufficient review of the ques- 
tion and its literature so all that will be attempted here is to bring for- 
ward three additional pieces of evidence in support of the above 
conclusion. ; 
First, as noted in the paper itself the value of the cutaneous capillary 
network for respiration will depend upon the permeability of the mem- 
brane through which diffusion must take place. The fact that this mem- 
brane is the epidermis and not the entire skin renders exact experimen- 
tation impossible. Nevertheless the experiments performed by Seelye 
indicate that the entire skin of lungless forms is much more permeable 
than that of those with lungs and it would be strange to urge that the 
difference in the cutis accounts for this for it is the lungless forms that 
have the thicker cutis. This point of structure is, according to Seelye, 
the only one of general distinction between the skins of the two types 
in question; a conclusion that it is hard to understand unless it is due 
to the presence of two European forms with lungs among those examined. 
A more trustworthy comparison would be one between forms that live 
in the same environment and in the case of Plethodon this is possible, 
for small specimens of Amblystoma punctatum and of Dztemyctylus 
vuridescens in its terrestrial stage of life are occasionally found along 
with Plethodon cinereus. The skins of specimens so found and of adult 
Plethodons of about the same length were examined all being submitted 
to the same procedure, v2z. the entire animal was fixed in Zenker’s fluid 
with fhe usual after treatment, then from similar regions of head, trunk, 
and tail, pieces from dorsal, ventral, and lateral aspects were sectioned 
perpendicularly to the surface. The only considerable and constant 
difference in the epidermis is one of thickness. To estimate this correctly 
several measurements in micra were made from each piece of skin and 
these were averaged. Finally the figures thus obtained for each of the 
areas investigated were averaged to obtain a figure that would fairly 
