HarleY;, on Cutaneous Respiration. 
149 
to be covered with a layer of epithelium cells^ and in their 
centre could be distinctly seen a small aperture not unlike 
that observed in some stomates. The question at once pre- 
sented itself, " May not these organs in the skin of the frog 
which so strikingly resemble the respiratory organs of plants, 
have a similar function to perform?'^ Dr. J. Davy"^ has 
pointed out that the pulmonary arteries of some of the 
Batrachia divide into two branches, one of which goes to the 
lung — the other, very little smaller, to the cutis, and is exten- 
sively ramified among the follicles. The veins rising in this 
position are said to convey back arterial instead of venous 
blood. Before entering into the consideration of this ques- 
tion, I shall first as briefly as possible describe the structure 
of the organs alluded to. 
It being very difficult to detach the epidermis from the cutis 
vera of the frog's skin in the ordinary way, I put the body of a 
frog recently dead into water at a temperature of about 80° or 
90° cent. ; in a very few seconds the hot water induces a state 
of rigor caloris which lasts from twenty-four to seventy-two 
hours ; after a short immersion the animal is transferred to 
a vessel containing cold water, and kept there during several 
hours. The epidermis gradually detaches itself from the 
cutis vera, and can be very readily peeled ofi". A small por- 
tion obtained in this manner, when examined with a power 
of about 70 diameters, looks like a fenestrated membrane. 
It is seen to be pierced by a great number of openings vary- 
ing in size from to -/^ mm. in diameter, and of a more 
or less rounded shape, as represented at PI. VI, fig. 2. These 
openings are of so considerable a diameter that if the prepa- 
ration be held between the observer and the light, they are 
distinctly visible to the naked eye. When magnified with a 
high power of 200 or 300 diameters, they are seen to be 
covered with a layer of tesselated epithelium, which is appa- 
rently continuous with the most superficial layer of the epi- 
dermis. Each of the tesselated epithelium-cells constituting 
the covering has a well-marked nucleus (Pk VT, fig. 1), and 
in the centre of this layer or near it is a cell, dift'ering some- 
what in shape from the others, in being rounded, while the 
rest are more or less polygonal. The circular cell diff'ers 
still further from the others in having a small aperture 
instead of a nucleus ; it measures on an average mm. in 
men, as I imagined at that time that I was the first who had observed them. 
Since then, however, I have found that tlie honour of their discovery belongs 
to Dr. Ascherson. 
* 'Researches, Anatomical and Phj/siologica),' vol. i, p. 111. 
