Zool.— Vol. I.] RITTER—DIEMYCYTLUS TOROSUS. 77 



have seen (not included in the nine above mentioned) was 

 60 mm. long. As a very large number of old larva? and 

 young adults have come under my observation, I think it 

 safe to assume that the 60 mm. one is about the maximum 

 size attained by the larvaj; in other words about the maxi- 

 mum attained during the first three-quarters of a year of their 

 lives; i. e., from March to October inclusive, which may be 

 taken as the average larval period. The next larger size 

 that I have found in the fall have had a length of about 80 

 mm. I therefore conclude that these specimens are in their 

 second year — are about one year and eight months old. 



As I have never seen specimens of this size in which the 

 external sexual characters were developed, I conclude fur- 

 ther that sexual maturity is not reached till after the second 

 year. How much after I have no satisfactory means of 

 judging; but comparing the smallest sexually active males 

 observed with the specimens supposed to be approaching two 

 years of age, I think it probable that the males ordinarily 

 become capable of doing their part in the propagation of the 

 species when they are three years old. 



The points of chief importance in the section now under 

 treatment are: (1) those relating to the habits of life; (2) 

 those relating to seasonal changes in structure; and (3) 

 those relating to secondary sexual differences. Of course 

 it will be neither desirable nor possible to keep these dis- 

 tinct in description and discussion. 



1. Habits. — The first point concerning the habits of the 

 adults to which I would direct attention is the fact that the 

 most strictly terrestrial -period of life is that immediately 

 following metamorphosis. 



In view of the notably aquatic habit of the animals for a 

 considerable portion of their adult lives, it has been sur- 

 prising to me to find that they are exceedingly particular 

 about getting out of the water as soon as the metamorphosis 

 is complete. In fact, if they are so situated that they can- 

 not get out by the time their larval characters, the gill-stubs 

 excepted, are gone ; or if after they have once left the 

 water they are immediately put into it again and are not 



