150 
Harley, on Cutaneous Respiration. 
diameter. The small aperture is of a peculiar triangular forai 
(P1.VI_, figs. 1, 3)^ as described by Asclierson^"^ seventeen years 
ago^ not at all unlike the shape of a leech-bite. On examining 
this aperture minutely (which is easily done with a portion of 
the superficial layer of epithelium detached from the rest of the 
epidermis)^ its sides are found to form three small triangular 
fiaps^ or valves^ which by their juxtaposition completely close 
the opening. In some specimens the valves are retracted, 
and the little gateways appear wide open; the patulous 
condition of the apertures is, however, not the one most 
usually observed. Mr. Huxleyf has described the trifid 
apertures as being disposed between three epidermic cells, 
and not as a peculiar structure in the centre of a cell 
differing in shape from the others forming the epidermic 
covering of the skin. I have examined this point very care- 
fully, and it appears to me that this gentleman has erred in 
supposing that the triangular opening is disposed between 
three epidermic cells ; had he examined the most superficial 
layer of the epidermis detached from the rest, he would 
easily have detected the peculiar circular cell with the open- 
ing in its centre. It may here be remarked that, if the 
epidermis in connection with the cutis vera, be placed under 
the field of the microscope, it is exceedingly difficult to dis- 
tinguish the superficial layer, and next to impossible to de- 
tect the aperture in the central cell. The observer would do 
well, therefore, in his examination of these structures to 
follow the plan given above. 
If the most superficial layer of the cutis vera of the frog 
be examined with a low power, it is seen to contain, like the 
epidermis, a number of perforations, which, by transmitted 
light, resemble so many windows in a dark ground (PI. YI, 
fig. 5) . Some of the windows appear as if partly closed by a 
curtain, while in others the occlusion is complete. The 
curtain, I presume, is nothing more than a portion of the 
lining membrane of the passage, accidentally detached in 
tearing away the epidermis, &c. The passage just spoken of 
is narrower at its mouth than at its base. It leads a short 
way into the corium, and then abruptly ends in a blind sac. 
Dr. Ascherson, in the paper already cited, says that, on 
making a transverse section of the skin, he failed to detect 
any duct leading from the cavity in the cutis vera to the 
triangular aperture on the surface of the epidermis, although 
* Mliller's 'Archiv/ 1840, p. 15. 
f Article " Tegumentary Organs," Todd and Bowman's ' Cyclopsedia of 
Anatomy and Physiology/ p. 500. 
