160 University of California Publications. izoology. 



Even in the unswollen tail it measures about one-sixth of the 

 vertical diameter of the organ, but in the swollen ones it may 

 reach one-fourth of this dimension, as in the one shown in tig'. 4. 

 The thickness decreases from a point just outside the median 

 dorsal line, and becomes of ordinary depth at the meeting of the 

 dark upper and light lower surfaces. From the caudal border of 

 the anus to within nearly a millimeter of the tip this thickened 

 skin sits like a saddle astride the tail's back. 



A median dorsal groove occurs on the inner surface of this 

 skin. The whole of the surface exhibits a marked granular 

 appearance to the unaided eye, which is due, as can be seen with 

 a hand lens, to the presence of distinct bodies so closely crowded 

 together that they become five-, six- and seven-sided in outline. 

 On cross section of the skin these bodies appear as columns about 

 four times higher than wide, flattened at the inner ends, the spares 

 between the outer ends being filled with smaller cylindrical and 

 spherical bodies, fig. 4, PL XVI. These structures prove to be 

 greatly enlarged epidermal glands. Each one is made up of large 

 granular cells, and opens to the exterior by a short duct. The 

 smaller cylindrical and spherical bodies mentioned in the preced- 

 ing paragraph are also glands. As will be seen in fig. 4, the 

 large glands on the dorsal side of the tail grade into the small 

 ones which occur on the ventral side of that organ, and, less 

 thickly crowded on almost every other portion of the body of the 

 animal. In the swollen tail they are closely set together and 

 filled to the utmost with secretion, while in the unswollen one, as 

 shown in fig. 5, they have discharged and new glands are forming. 



In neither Diemyctylus nor Batrachoseps do we find any such 

 development of tail glands. The skin everywhere of these species 

 is richly provided with glands, and in Diemyctylus these are large 

 and abundant in certain regions of the back, but they are not 

 massed upon the tail. 



It is evident from a comparison of the tail glands of Plethodon, 

 both with those from other regions of the body of the same animal 

 and with those of other species, that we are dealing here with 

 structures widely distributed among the Batraehia. Numerous 

 authors have described them in many species of both urodela and 

 anura. Their massing along the ridge of the tail is not uncommon 



