HARRIS : CRAYFISHES GENUS CAMBARUS. 95 



of the ditch. A number of the taller ones, but more usually 

 the lower ones, had their tops sealed over. The "chimneys" 

 were evidently built up of "small pellets of mud laid on in a 

 single course, the fusing together of the pellets depending 

 somewhat upon the dryness of the ground when the structures 

 were erected." 



Of a burrow of C. diogenes in the neighborhood of Washing- 

 ton, D. C, he says : " Right on the bank of the stream I opened 

 another ; it only passed down eleven inches, when it terminated 

 in a chamber about as big as my two fists, and placed at the 

 side. It was below the water-level, and contained a fine living 

 specimen of C. diogenes.'' 



The "sealing-in" of the burrow, he found, was very thorough, 

 the top being as thick as the walls, inside passage terminating 

 "in a smooth, concave, hemispherical end." How and why 

 the crayfish seals its burrow, he saj^s, is as yet unexplained. 

 "Possibly it may do this by backing up the burrow, and, by 

 turning round and about, manipulate the moistened clay or 

 mud into place by the use of its lateral tail fins and telson." 

 As to the reason for sealing, he suggests that it may be that 

 the orifice is sealed to prevent the upper rim from falling back 

 into the burrow, to shut out rain or rising w^ater, to prevent 

 the attack of enemies, or while the parent is laying her eggs at 

 the bottom of the burrow. 



Schufeldt, like Tarr, believes that the chimney is not the re- 

 sult of design on the part of the animal, but is simply the most 

 convenient and safe way of getting rid of the pellets. 



Hay ('96) , after giving some of the older observations, says : 

 "The subterranean tunnels may sometimes be found to extend 

 for several feet, and, as the animal frequently excavates them 

 at some distance from water, they must reach a depth great 

 enough to supply moisture sufficient for the need of the animal. 

 During the dry months of the summer, however, they seem to 

 lie in the end of their burrows in a sort of stupor. I have seen 

 them fall from the end of an excavation, apparently lifeless, 

 but capable of moving when put into water. In the early spring, 

 when they come forth to breed, is the only season when they are 

 a noticeable member of our fresh-water fauna. They move 

 about chiefly at night, though I have frequently taken numbers 

 of them from ditches and small streams on bright, sunny days. 



