Zool.— Vol. I.] RITTER—DIEMYCTYLUS TOROSUS. 109 



mm. in length. From numerous measurements the average 

 length at metamorphosis appears to be about 47 mm. 



The first visible evidence of the impending metamorphosis 

 consists in a very slight duskiness over all the dorsal parts 

 of the animal outside the black bands, and a simultaneous 

 tinging of the ventral surface with the yellow that will char- 

 acterize this region of the adult. 



These color changes become rapidly more pronounced, 

 particularly as regards the dorsal side, where the brownness 

 of the head and neck region is soon especially noticeable. 

 The black bands of the back diminish in distinctness pari 

 passu with the increasing general duskiness of this region, 

 until by the time metamorphosis is complete they have disap- 

 peared entirely. Figs. 4 and 5. 



The general dark color of the transforming larva is due 

 to the presence in the epidermis, and for the most part in 

 its outer, or corneous layer, of fine granular, diffuse pig- 

 ment; while, as previously stated, the characteristic larval 

 pigment is contained in large, usually much branched sub- 

 epidermal, connective tissue cells. 



The precise histological changes that occur in the integu- 

 ment during metamorphosis I do not enter upon in the present 

 contribution. 



The first change of form which takes place consists in 

 the beginning reduction of the dorsal lobe of the tail fin. 

 As already stated, and as shown by fig. 7, this extends 

 almost to the head in the full-fledged larva. It is in its an- 

 terior portion that the diminution first becomes noticeable; 

 but soon it is observed to be distinctly lower in the tail re- 

 gion proper; and by the time the animal is ready to leave 

 the water almost all the previously transparent part of the 

 tail, i. e., the whole of the true lobe, ventral as well as 

 dorsal, has quite disappeared, and the tail has become al- 

 most round in transverse section (figs. 4 and 5). 



The skin, entirely smooth during larval life proper, be- 

 gins to take on the granular structure characteristic of the 

 summer condition of the adult, almost as soon as the change 

 of color begins; and even before the gills have fully disap- 



