OliTMANN: THE CRAWFISHKS OF THE STATE OF PENNSYLVANIA 423 



food), but this is necessary only at long intervals (even for food it is not absolutely 

 imperative to go out frequently, see infra), and the stopper is easily removed. 

 huring winter a more effective stopper is provided liy tlie crawfish, and it remains 

 ftir three or four months shut up in its liole. 



The chief activity in ciiimney-building is in spring."" l>uring winter frost de- 

 stroys or damages the upper parts of the hole, and the rel)uilding necessitates a good 

 deal of work, and large mud-piles are accumulated in con.sequence (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 fresli 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 <'. diogenes, as we shall see, it is chiefly in midsummer that the 

 young l)egin 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 tlie warm season. 



( ienend activity again begins with older specimens late in the fall, and this has 

 a very interesting cause, and my attention was called to it Ijy Mr. V. K. Kdl}' of 

 rittsburgh, 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 fro.st. In sunnner these parts are abandoned and tlie 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 tiic fall the deeper, aban- 

 doned part of the hole (see PI. XLl, Fig. 7 at c), which fills up during the sunnner 

 with dirt, forming :it the bottom of the hole asoft. pulpy nuis.s, is reclaimed by the 

 crawfish in order to go deeper down out of reach of frost ; the nuid is consequently 

 removed, an<l the necessity of cleaning out these deeper pnrts of the hole is the 

 cause of the renewed activity in the autumn (PI. .\LI, 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 lUUo. The fall activity tnkes place 



"Young specimens begin first, as soon as the fro.st is out of the ground. New cliinineys of C. ilhgrmf were ecen 

 on March 23, 190.5, in Nine-Mile Kun, and the activity wasgeneial on April G, 190.'), ( K'cnfrew). Tlie limt signs of new 

 chimneys of C. iminnngnlni^is were seen at Edgewood I'ark on March 18, l!)(l."i (frost only partly out of the ground) ; the 

 activity was general on March ;51, (Colliers, W. Va.), and April I (Edgwood I'ark). 



