ORTMANN: THE CRAWFISHES OF THE STATE OF PENNSYLVANIA 493 
food), but this is necessary only at long intervals (even for food it is not absolutely 
imperative to go out frequently, see imfra), and the stopper is easily removed. 
During winter a more effective stopper is provided by the crawfish, and it remains 
for three or four months shut up in its hole. 
The chief activity in chimney-building is in spring.* During winter frost de- 
stroys or damages the upper parts of the hole, and the rebuilding necessitates a good 
deal of work, and large mud-piles are accumulated in consequence (4 to 12 inches 
high, 12 to 18 inches in diameter). But after the hole has been restored to a satis- 
factory condition work ceases, and in summer not much fresh mud is brought out. 
Occasionally new chimneys are seen in summer, and the activity may be resumed 
at any time if necessary. Besides young specimens remain active all through the 
summer. In C diogenes, as we shall see, it is chiefly in midsummer that the 
young begin to build their own holes. In the other species this may take place at 
any time from spring to fall, and thus the new and often very regular chimneys of 
small specimens may be seen at any time during the warm season. 
General activity again begins with older specimens late in the fall, and this has 
a very interesting cause, and my attention was called to it by Mr. F. E. Kelly of 
Pittsburgh, but I have confirmed it by subsequent observations of my own. It is 
evident that the deepest parts of the holes are occupied and used by the crawfishes 
only in winter; these parts go down to about three feet, and thus are entirely out 
of reach of the frost. In summer these parts are abandoned and the crawfish in- 
habits only the upper parts of its burrow. In digging for crawfish in summer I often 
followed the main hole to a considerable depth, finally discovering that this hole 
was filled with soft ooze and mud, and that no crawfish was in this part; further 
careful investigation generally revealed a side branch at a higher level, which was 
clear of mud, and here the crawfish was captured. In the fall the deeper, aban- 
doned part of the hole (see Pl. XLI, Fig. 7 at c), which fills up during the summer 
with dirt, forming at the bottom of the hole a soft, pulpy mass, is reclaimed by the 
crawfish in order to go deeper down out of reach of frost ; the mud is consequently 
removed, and the necessity of cleaning out these deeper parts of the hole is the 
cause of the renewed activity in the autumn (PI. XLI, Fig. 7). Before Mr. Kelly 
communicated to me his discovery of this fact I had not paid attention to it, but 
was able to verify it in the summer and fall of 1905. The fall activity takes place 
58 Young specimens begin first, as soon as the frost is out of the ground. New chimneys of C. diogenes were seen 
on March 23, 1905, in Nine-Mile Run, and the activity was general on April 6, 1905, (Renfrew). The first signs of new 
chimneys of C. monongalensis were seen at Edgewood Park on March 18, 1905 (frost only partly out of the ground); the 
activity was general on March 31, (Colliers, W. Va.), and April 4 (Edgwood Park). 
