40 



THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBARUS 



The number of moults necessary to increase the larva from the fifth stage 

 when about 20 mm. long to the autumnal larvae ranging from 30 to 63 and 

 averaging 54 is not known. The amount of increase at each moult above 

 tabulated was about 3 mm. In one case above cited a larva which had grown 

 only to 30 mm. in the autumn, when well fed quickly gained 4 mm. probably in 

 one moult. We might expect then an increment of 3 or 4 mm. at each moult, and 

 growth from the 20 mm. length of the fifth stage to the average autumnal 

 length of 54 mm. may have taken from 8 to 11 moults thus making an estimated 

 total of 12 to 15 moults the first growing season. The size reached was, how- 

 ever, evidently determined in part by food. On such basis it may have taken 

 even more moults to produce the large autumn young 60 and 63 mm. long. 

 And at all events the above larva 30 mm. long having been kept in a closed 

 aquarium should be disregarded in reckoning the average. Rejecting this the 

 average for the seven others reared in running water would be 57. To attain 

 this average size it may well have required at least nine moults after the fifth 

 stage. 



It seems then not improbable that this Astacus, under these conditions 

 moulted at least a dozen times while growing to a length of over two inches in the 

 first five months of its life. Four stageswere observed in the first two months 

 when the length had not extended to four-fifths of an inch, and probably twice as 

 many stages were necessary in the following three months to bring the length 

 up to over two inches. 



The only previous records of the rate of growth of young Astacus seem to 

 be those of Soubeiran, Chantran, and Steffenberg. Soubeiran ('65) from 

 measurements of a crayfish in a French crayfish farm concluded that they did 

 not moult more than once in the first year, and were 50 mm. long when one 

 year old. Chantran ('70) thought the young crayfish moulted five times in 85 

 to 100 days of July, August, and September and no more till the end of the next 

 April. The first moult was at ten days after hatching and the other four at in- 

 tervals of twenty to twenty-five days each. These results were modified by 

 his further studies, also in the laboratory, and later ('71) he stated the number 

 of moults iii the first summer was eight and that the temperature influenced the 



