474 MEMOIRS OF THE CARNEGIE MUSEUM 



the same conditions are established which were found in early spring. Males of the 

 first form prevail, and those of the second form are scarce, and generally of a small 

 size, between 30 and 40 mm. long. Specimens of less than 30 mm. in length are 

 very rare and represented by individuals of the last generation, which have not 

 been able for some reason to keep pace in growth with their l)rothers and sisters. 

 The males are sexually mature, and apparently the females likewise, as we shall 

 presently see. 



Copulation actually takes place now. 1 have quite often observed it in the field, 

 and made record of the following dates: September 5, 1906; September 28, 1905; 

 October 6, 1904 ; November 19, 1904. In addition couples were found apparently 

 preparing for copulation, but not in tlie act, on September 7, 1905, and September 

 30, 1905. Among the material collected by Mr. W. R. McC-onnell was a couple taken 

 in cojyuki on September 5, 1905. In captivity I observed copulation on SeptemVjer 8, 

 1905, and November 22 and 23, 1904, and I have found that it is very easy to 

 induce couples to copulate about this time (September, October, November), pro- 

 vided that one male and one female are put in the same jar. In no other part of 

 the year, and, what is more important, not even in spring (March, April, May) does 

 copulation take place, either in nature, or in the laboratory. All my attempts to 

 induce specimens to copulate in spring have l)een in vain, and, of course, in June, 

 July, and part of August, copulation is impossible, the males not being in condition. 

 Copulation may occur in August, males of the first form being present, but possibly 

 the females are not in proper condition before September on account of the delay 

 of the spring moult. The smallest female seen in copulation was 43 mm. long; 

 and she undoubtedly belonged to the generation born in spring, thus establishing 

 the fact that the females like the males are generally sexually mature at the end of 

 the first summer, and that they are able to produce eggs the next spring. {See 

 above. The smallest female with eggs was 40 mm. long.) 



The above observations and conclusions are founded upon the comparison of 

 large numbers of individuals, but no single specimen has been followed through all 

 the different stages of , seasonable development. But to a certain extent it is possi- 

 ble to ascertain the changes through which one and the same individual has to go, 

 and to lay down its life history. 



The young Cambarus obscunis is hatched at the end of May or tlie Iteginning of 

 June, from eggs laid in April. The young stay with the mother under the abdo- 

 men of tlie latter, for a short time (about a week) ; then they shift for themselves 

 and develo() during the sunniier rather quickly, moulting repeatedly.'' In Septem- 



" Compare Andrew's observatious on C. limoaus (1904, p. 190, ff. ) : he liistinguishes seven larval stages (each be 

 ginning with a monlt), from the hatching, end of May, to the middle of July, when a length of 29 mm. was reached. 



