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THE AMERICAN NATURALIST. [Vol. XXXVIII. 



preceding tables though they were four months older. But this 

 additional time was autumn and winter and it would "seem 

 probable that the crayfish of Table III not being as well fed as 

 the others had not grown quite as fast during the summer and 

 had then remained stationary. Though they were kept in a 

 warm room they were in running cold water. 



The above twenty crayfish of table III were then kept in the 

 same conditions during the rest of the Winter, Spring, Summer 

 and Autumn and until December 5, 1903. The only two sur- 

 vivors were both females and at that time, being 1 8 months old, 

 gave the following measurements. One was 70 mm. long and 

 16 mm. wide : the other 79 mm. long and 20 mm. wide. Since 

 last measured, a space of ten months including a summer, each 

 had probably doubled its length. 



These two were left in the same surroundings, except when 

 removed for breeding as below described, and measured again 

 July ist, 1903, when 25 months old. One was 79 mm. long and 

 20 wide, and the other 76 mm. long and 20 wide. The latter 

 was clean and bright and the former dark and dirty as ni winter 

 so that we infer the smaller one had recently moulted and added 

 6 mm. or about to its length and \ to its width. 



During their third summer these two females were kept with 

 the young of Table I and thus had better f6od conditions. Only 

 one survived till October 6th and then had a length of 90 mm. and 

 a width of 24 mm., while its tail-fan expanded 43 mm. It had 

 thus gained more than 10 and perhaps as much as 14 mm. in 

 length or added \ to nearly \ to its length. 



Summarizing the above data we see that the young of 

 C. affinis reared in the above conditions of captivity hatch in 

 May from eggs 2 mm. in diameter as larvae 4 mm. long and 

 there pass through stages of 4^ 8, 12, 15-18, 21 and 29 mm. 

 during the first two months. During the next three summer 

 months they increase to an average length of 40 mm. but may 

 grow as long as 62 mm. During their first winter they may, 

 probably, not grow at all ; but in the second summer they may 

 reach a length of 70-80 mm. In the third summer the length 

 may become 90 mm. as indicated by the sole survivor at 

 28 months. 



