THE YOX^NO OF THE CRAYFISHES ASTACUS AND CAMBARUS 



63 



Tlie active third larviB becoming independent lived some eighteen days in 

 all before moulting again to pass into a fourth stage and these in turn were 

 followed through more stages till eventually adults were reared in the labor- 

 atory. Without describing the gradual changes of the early larviB to the details 

 of adult form we may now give a more complete record of the rates of growth 

 of young crayfish than has hitherto been possible as a number of new observa- 

 tions have been added to those previously published, Andrews ( :04), and certain 

 points as to the period of sexual maturity determined. We will give certain 

 facts as to the number of moults, as to the rate of growth, as to the develop- 

 ment of the external male organs, as to the ratio of the sexes and as to the ar- 

 rival of sexual maturity and the ability to l)reed in captivity. 



Observations made upon the young of a single female which laid March 2S, 

 IDO.?, and whose eggs hatched May 18, 1903, gave the times of moulting and 

 rates of growth of the larv;e represented in the following table: 



These same young were kept till October 6, 1903, without observation and 

 the eight survivors then measured as follows : 62, 55, 53, 49, 50, 45, 43, 41 

 mm. in length. The average is nearly 50 and as far as can be judged from the 

 above table such a large larva as that measuring 29 mm. in the seventh stage 

 would probably have passed through at least four or five moults to become the 

 large one 62 mm. long and smaller larvaj would have required as many or 

 more moults if the increment was as large as in passing from the sixth to the 

 seventh stage ; but if the increase was the average for the above seven stages, 

 scarcely 4 ram., then at least six more moults may have taken place. Other 

 data show that the rate of growth is very different in individuals and in some 

 cases seemed to depend directly upon food supply so that the number of moults 

 during the first summer is probably not by any means constant but different 

 in individuals. However, we are sure that at least seven stages may be passed 

 through and probalily eleven to thirteen larval stages may occur in the first sum- 

 mer of the creature's life outside the egg. Yet data given below show that the 

 larvjp may remain but 20 mm. long in the fall, owing, probably, to insufficient 

 food arresting them when in the sixth stage. 



