THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBARUS 65 



The third group of 20 ranged from 23 to 56 with an average of 35. 



The fourth group of 26 ranged from 20 to 47 with an average of 36. 



The fifth group of only 7 ranged from 37 to 51 with an average of 43. 



The sixth group of 30 ranged from 36 to 57 with an average of 45. 



The large size of the crayfish in the first group was undoubtedly due to 

 greater care taken to feed them and the differences in other groups were prob- 

 ably due to differences in food supply and also in temperature. 



Judging from the above 101 measurements the young four months old may 

 vary in length from 20 to 62 mm. but while the average of all was 41 mm. the 

 average of different experiments ranged from 35 to 50. 



We may then expect this crayfish to be nearly two inches long in the autumn 

 of its first year of life. 



Measurements made in the autumn and again in the next spring showed 

 that there was no growth from October to May, except in rare cases in which 

 a moult occurred in early spring. The crayfish thus started in their second 

 summer of life with a length of nearly two inches and were the same size 

 when twelve months old as when four months old. 



The rate of growth in this second summer may be inferred from some few 

 measurements made in October upon crayfish reared from eggs laid in the 

 laboratory and measured then, when sixteen months old. Of five larvae measur- 

 ing May 26, 1904, 62, 55, 53, 50, 62 mm. the three survivors in October, 1904, 

 measured 75, 80, and 72 mm., an average of 76 mm. From the average, 58, of 

 the above five to the average 76 of the three survivors there was an increase 

 of 18 mm., or a gain of 30 per cent in length in this second summer. And 

 records showed that one of these larvae had grown from 62 to either 75 or to 

 82, that is added 13 or else 20 mm. to its length, or increased 21 per cent or 

 else 32 per cent. 



Another group of young left three survivors of 56, 70, 75 mm., or on the 

 average 67 mm. when 16 months old to represent the seven which were 40-45 mm. 

 long when twelve months old; they had thus probably added 25 mm. or gained 

 more than 50 per cent in the second summer. 



A third group of young, twenty in number, ranging from 23 to 56 mm. 

 when twelve months old, left only two survivors at sixteen months, which 

 measured 70 and 79 mm., or an average of 74 : there was thus an increase from 

 the average 35, of 39 mm. But records of the individuals showed that the few 

 survivors were probably 43 and 56 mm. long in the spring and had grown only 

 23 and 27 mm. in each case which would be an increase of 53 per cent and of 63 

 per cent. 



The above few data indicate a growth in the second summer of sometimes 

 50 per cent of the length; that is a crayfish two inches long the end of the first 

 summer may be expected to be three inches long the end of the second summer, 



