ORTMANN: THE CRAWFISHES OF THE STATE OF PENNSYLVANIA 473 
very large females are rare in the latter part of June and in July, and do not become 
more abundant till the beginning of August. In addition we now have a new genera- 
tion of young crawfishes, hatched at the end of May and beginning of June. After 
these have left the mother it is difficult to get them. ‘They are too small, and are 
often overlooked, and if captured in the net, are able to escape through the meshes. 
But I have seen them at this time, although the first recorded captures are as late as 
July 10, 1900 (by Dr. D. A. Atkinson), size 26 mm., and July 24, 1905 (by myself), 
size 21 to 23 mm. This young generation is easily distinguished from the rest by 
its size, being considerably less than 830 mm. in length. The minimum length of 
crawfishes in spring is 31 mm. in the case of males and 27 mm. in that of females. 
In the middle of July further changes occur. A new period of moulting begins 
for the medium-sized and older individuals, which is chiefly noticeable among the 
males, since they now again assume the first form. The earliest date for the new 
males of the first form is July 11, 1905 (Tionesta and Spartansburg). Altogether 
four individuals were taken, all of which had soft shells, showing the fact that they 
had recently moulted. Further dates are July 24, 1905 (Deer Lick), July 
25, 1906 (Russelton), July 26, 1904 (Derry), July 27, 1906 (Shousetown), and 
then in August and the following months they regularly occurred. At first 
these males of the first form are scarce, but they become gradually more fre- 
quent, till finally at the end of September and in October almost all males have 
assumed the first form. This also holds good for the new generation born at the 
end of May and the beginning of June. These young ones are about 20 to 23 mm. 
long in July; in August I have specimens from 24 to 39 mm. in length; in Sep- 
tember from 26 to about 50 mm. in length. About this time this generation be- 
comes obscured ; for it seems that the rate of growth of the young crawfishes is very 
different in different individuals, some gaining during June, August, and September, 
only about 15 mm. in length, others more than twice that length. They are about 
10 or 11 mm. long when they hatch. The same fact was observed by Andrews 
(1904, p. 202) in C. limosus, with even greater differences in size (the length of the 
young of the same generation in October being between 22 and 60 mm.). 
It is ascertained from the above observations that young specimens, born in 
early summer, already at the end of the first summer (September and October) 
reach a size sufficient to prepare them for propagation, and the males of this genera- 
tion as a rule show this by changing into the first form. The smallest male of the 
first form, collected by myself in fall (October 6, 1905), is a specimen from Kittan- 
ning, 88 mm. long, but specimens from 40 to 50 mm. long, and undoubtedly belong- 
ing to this generation, are quite abundant at this time. Thus we see that by October 
