92 CALIFORNIA ACADEMY OF SCIENCES. [3D Ser.. 



their search after food, to spend much of this period on 

 land. 



It would, I believe, be about as easy to establish the prop- 

 osition that the annual period of sexual activity is deter- 

 mined by life habits primarily induced through environ- 

 mental influences, of which those pertaining to food and 

 moisture are probably most important, as it would to establish 

 the opposite proposition; viz., that the life habits and their 

 accompanying structural characters are secondary to sexual 

 activity. But this is a very difficult problem, though per- 

 haps not wholly unsolvable. 



3. Sexual Differences. — The characters distinctive 

 of the sexes have been mostly adverted to already, though 

 indirectly. 



Until sexual maturity is reached there is, so far as I have 

 determined, no way of distinguishing them by superficial 

 inspection. Males and females are alike papillated and 

 narrow-tailed. 



As already pointed out, the females never leave this con- 

 dition. Whether this is due to a failure on their part to take 

 on the broad tail and smooth skin, because these are in real- 

 ity male characters, or to the fact that they are less aquatic 

 in their tastes and habits, or to some other cause, I do not 

 know. My observations do, however, lead me to believe 

 that on the whole the males are more fond of the water than 

 are the females. 



The great development of the lips of the male cloaca as 

 compared with those of the female during the breeding 

 season is very distinctive. In addition to the great en- 

 largement of these parts, there is a dark band extending 

 down from the general dark ground color of the dorsum 

 and sides of the body on the cloaca almost to the ventral 

 edge of the lips (fig. 2). The female cloaca never becomes 

 enlarged to any extent, and is always without the lateral 

 bands. 



During the breeding period there is developed on the in- 

 ner surface of each femur in the males a patch of epider- 

 mis harder and more corrugated than in adjacent parts, and 



