Zool— Vol. I.] RITTER-DIEMYCTYLUS TOROSUS. 89 



another condition, an instance of which is illustrated by 

 fig. 1, absolutely no trace of papilla? is to be found. 

 From the comparative rarity and large size of speci- 

 mens of this kind, I conjecture that these individuals have 

 arrived at about the extreme age to which the species 

 attains. 



I must also call attention to the faded out appearance of 

 the two last mentioned specimens. It looks very much as 

 though they were actually sun-bleached. Individuals of 

 this color are by no means rare. In fact, specimens are 

 frequently seen which are more conspicuously light colored 

 as they are seen in the water than those here figured appear 

 to be. Prof. Cope mentions that "in the rough specimens 

 the brown becomes almost black;" and that "in smooth 

 specimens the brown is pale, and has an olive tinge." In 

 general this is true, but it is by no means always the case 

 that the rough ones are almost black. As much as can be 

 said is that the darkest color ever attained is by the rough 

 ones, and that the lightest color reached is by the smooth 

 ones. This color variation takes place in the males alone, 

 the females retaining with considerable constancy their char- 

 acteristic seal brown color. 



The decidedly dark color of the side of the body, as 

 compared with other parts, shown in fig. 2, will be no- 

 ticed. This condition heightens the impression above 

 mentioned, that the light color is due to sun bleaching — 

 and I may say that specimens of this kind have been seen 

 more frequently than elsewhere in the North Berkeley reser- 

 voir, which, as already said, is fully exposed to the sun. 



I have previously stated that the papillated, narrow-tailed 

 condition may be again assumed by the smooth-skinned, 

 broad-tailed specimens. Of this I have positive evidence 

 from experiments with animals kept in confinement. Last 

 winter I placed some two dozen specimens, most of which 

 were males with well developed tails and much reduced pa- 

 pilla;, in a terrarium in the laboratory. The most of them 

 are still living (July 3), but they are now all like the one 

 shown in fig. 2. The tails are reduced to the minimum in 



