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



depth, and the epidermis is nearly at the maximum of papu- 

 lation; and I am convinced by numerous observations on 

 animals in nature, particularly by those made during the 

 present spring and summer, that the same reversion takes 

 place normally. I have recently (in midsummer) examined 

 many males, not only at the reservoir but also from several 

 streams in the vicinity, and have not found one which pos- 

 sesses the smooth skin. 



Not only this, but it can actually be seen that the papillae 

 are growing out on skins that were previously smooth. The 

 black tips, at first projecting but slightly above the surface, 

 make their appearance while the general groundwork still 

 shows the smoothness and softness which characterize it 

 when the papillae are wholly absent. The feel to the hand 

 of the condition here described is quite different from what 

 it is at any other period during the animal's life. 



It will be remembered that Gage's conclusion concerning 

 D. viridescens is "that the coloration is dependent neither 

 on food, season, nor environment, but is normal for a given 

 period of life only," since he found that the red coloration 

 changes to the viridescent whether the animal enters the 

 water or not, and that it is not resumed even though viri- 

 descent specimens are kept out of water for long periods of 

 time. Professor Gage appears to be particular to limit his 

 denial of the potency of environmental change in this case 

 to its influence on color. What he thinks about the cause 

 of the change in the form of the tail, for example, which 

 accompanies the change of color, he does not tell us. Con- 

 cerning the replacement of a ciliated by a non-ciliated oral 

 epithelium, as the animals change from the atrial to the 

 aquatic mode of respiration, he remarks, however, that 

 " the change has something the character and certainty of 

 a simple chemical reaction." 



As regards D. torosus, the facts above pointed out, viz., 

 that the repapillation of the skin and reduction of the tail 

 take place even though the animals do not leave the water, 

 might seem to indicate that even structural changes in this 

 species are " normal for a given period of life," and are not 



