88 CALIFORNIA ACADEMY OF SCIENCES. [3D Ser., 



the structure of the skin, although this does not appear 

 quite as clearly in the figures. 



I refer, of course, to the papillation and the greater hard- 

 ness of the epidermis of the land-dwelling form. The 

 " granulation " of the skin, as it has been usually designated, 

 pertains, when the condition is at the height of its develop- 

 ment, to almost the entire surface of the animal. It is, 

 however, most pronounced on the back and part way down on 

 the sides of the body. In these regions the papilla; are both 

 larger and nearer together than elsewhere. They are least 

 developed about the end of the nose, on the tail, particularly 

 along its ventral side, on the inner surface of the limbs, and 

 on the soles of the hands and feet. They are also always 

 considerably less numerous and lower on the belly than on 

 the back. 



Each papilla is crowned by a cap of deeply pigmented 

 cells, in the middle of which is the opening of a gland. 

 Figure 13 represents a surface view of a small piece of 

 sloughed epiderm. It is not my intention to enter into a 

 histological description of the epidermis at present, but I 

 may say that there can be no doubt about the presence of 

 openings at the summits of the papilla;. Even a superficial 

 examination of microtomic sections of the skin is sufficient 

 to convince one of the fact. 



The papillae make their appearance in all individuals, males 

 as well as females, some time before metamorphosis is com- 

 plete. The females retain them throughout life, so far as I 

 am able to determine, while they disappear almost entirely, 

 in many cases absolutely, from males when the aquatic habit 

 is fully resumed. My belief is, though the proof of this is 

 not complete, that in general the papilla; disappear more and 

 more as the animals grow older. 



In many specimens, a good example of which is presented 

 by fig. 2, while the epidermis is perfectly smooth, i. e., 

 is wholly without the papilla;, there are frequently seen a 

 great number of light colored spots corresponding in size 

 and distribution with the papilla; when these are present. 

 They are evidently remnants of the papilla;. In still 



