64 THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBAKUS 



After October there were no moults till the following warm season, the 

 lengths remaining constant during the winter. Just as the growth in the first 

 summer was restricted to the five months of May, June, July, August, and Sep- 

 tember, so in the second summer there was an increase of 25 mm. during that 

 time and though the moults were not observed there may well have been four 

 or five during this second summer. In a few exceptional cases a moult took 

 place in the early spring before May and a gain of 6 mm. was observed then. 

 After a second winter of no moults there followed a third summer of growth in 

 which a single observation showed that a specimen 70 mm. long December, 

 1902, was 76 mm. long July 1, 1903, an increase of 6 mm. probably due to one 

 moult. As this same individual increased to 90 mm. by October, 1903, it prob- 

 ably moulted two or three times or in all three or four times during this third 

 summer. 



We thus have evidence for seven and probably as many as twelve moults 

 the first summer, four or five in the second summer, three or four in the third 

 summer, and in the fourth summer perhaps only one or two moults to judge 

 from a single case of 8 mm. increase. 



Without reference to the number of moults, observations upon the amount 

 of growth of young crayfish hatched from eggs laid in the laboratory and kept 

 under various artificial conditions in the laboratory, were made and are re- 

 corded below as a substitute for data never yet obtained as to the rate of 

 growth of American crayfish in the open. 



The following list gives the length in millimeters from tip of rostrum to end 

 of telson of 101 young hatched in May, kept in six different tanks in different 

 years and under somewhat different conditions and measured in October when 

 four months old. 



I. 62, 53, 53, 49, 50, 45, 43, 41. 



IT. 60, 59, 52, 52, 45, 39, 40, 33, 30, 22. 



III. 41, 38, 24, 56, 32, 44, 43, 39, 39, 33, 35, 36, 32, 34, 30, 23, 30, 29, 27, 32. 



IV. 47, 39, 33, 27, 20, 23, 31, 38, 30, 31, 28, 30, 35, 35, 35, 34, 36, 42, 46, 52, 46, 

 45, 46, 41, 39, 40, 36. 



V. 43, 51, 41, 49, 43, 37, 38. 



VI. 55, 43, 55, 48, 38, 50, 40, 40, 53, 46, 40, 42, 40, 43, 50, 45, 44, 48, 50, 49, 37, 

 57, 44, 45, 43, 46, 46, 36, 38, 38. 



It is obvious that there was great individual difference in size attained in 

 the first four months of life both under different conditions and when kept in 

 apparently the same conditions, but of course subject to different chances of 

 food supply even in one tank. 



The first group of eight survivors ranged from 41 to 62, with an average 

 of nearly 50. 



The second group of 10 survivors ranged from 22 to 62 with an aver- 

 age of 43. 



