Harley^ on Cutaneons Respiration . 
151 
he had little doubt that some channel of communication 
existed between them. Mr. Huxley^ in his able article just 
quoted^ has given a diagram in which the canal leading from 
the triangular mouth to the cutaneous gland is represented 
as a very small tube^ with a diameter not greater than that 
of the trifid opening. In the specimens of skin which I 
have examined^ the canal was very wide^ in fact it seemed to 
possess the same diameter as the large opening, seen on the 
surface of the epidermis, covered with epithelium. The 
minute triangular aperture appeared to me to be only a small 
door opening into a wide passage, which passage conducted 
directly into the cavity beneath. I imagine it possible that 
Dr. Ascherson failed to detect the canal, in consequence of 
his searching for a fine duct having a diameter equal to the 
trifid aperture, instead of one equal to the large perforation 
in the epidermis. 
I have CEtrefuily searched for a fine tube as represented by 
Mr. Huxley, but have not yet been able to detect the slightest 
trace of one."^ At first sight, the size of the duct appears to 
be a matter of secondary importance; but when it is re- 
membered that we are at present attempting to deduce a 
knowledge of the function from the peculiar structure of the 
organ, it is at once observed to be a point of considerable 
moment. A small tube, although answering admirably for 
the transpiration of liquids, would greatly retard the free 
interchange of gaseous fluids. When we have minutely con- 
sidered the peculiar structure of the cutaneous follicles in the 
skin of the frog, we shall next attempt to show in what 
manner they diff*er from the ordinary forms of sudoriferous 
glands, and how they would seem to be constructed for per- 
forming the function of cutaneous lungs. 
The outline, as well as the relations of this passage and 
terminal cavity, can be tolerably easily studied in a transverse 
section of a portion of skin which has been preserved during 
a few days in a solution of chromic acid. Such a section is 
represented at PI. VI, fig. 6. The size of the cavities varies 
very considerably ; some are nearly twice as large as others. 
They are lined with a layer of tesselated epithelium, the nuclei 
of which, on the addition of acetic acid, come distinctly 
into view. Some of the cavities appear empty, or contain, as 
previous observers have said, only a clear fluid ; while others 
are full of a matter somewhat resembling mucus. f The wide 
* Since this paper was in type I have found tlmt Dr. Hensche noticed 
that the duct was wider than the orifice. ' Zeit f. Wiss. Zool.' vol. vii, p. 276. 
t Hensche states that they contain 30 — 40 or more polyliedral cells. These 
cells were probably those of the epithelial layer lining the cavity. 
