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 brothers and sisters. 
The males are sexually mature, and apparently the females likewise, as we shall 
presently see. 
Copulation actually takes place now. I 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 the act, on September 7, 1905, and September 
30, 1905. Among the material collected by Mr. W. R. McConnell was a couple taken 
in copula on September 5, 1905. In captivity I observed copulation on September 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 been 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 obscurus is hatched at the end of May or the beginning of 
June, from eggs laid in April. The young stay with the mother under the abdo- 
men of the latter, for a short time (about a week); then they shift for themselves 
and develop during the summer rather quickly, moulting repeatedly.” In Septem- 
7) Compare Andrew’s observations on C. limosus (1904, p. 190, ff.) : he distinguishes seven larval stages (each be- 
ginning with a moult), from the hatching, end of May, to the middle of July, when a length of 29 mm. was reached. 
