OF THE UNITED STATES 57 



the side walls. Inside, the cylindrical passage was as smooth 

 as usual, and terminated in a smooth, concave, hemispherical 

 end. 



As to the manner of building, Mr. J. De B. Abbott gives a good 

 account as cited by Faxon. The crayfish is seen to emerge par- 

 tially from its burrow, bearing "on the back of its right claw a 

 ball of clay mud, which, by a dexterous tilt of the Tlaw, was 

 placed on the rim of the chimney. Then the crayfish remained 

 perfectly quiet for a few seconds, when it suddenly doubled up 

 and dropped to the bottom of its burrow. There elapsed some 

 three or four minutes between each appearance; but every time 

 it came, it brought a ball of clay and deposited it in the manner 

 I have described. About two-fifths of the balls were not placed 

 with sufficient care, and rolled down outside of the chimney." 

 Professor Faxon remarks further that "Dr. Abbott believes that 

 the closing of the orifice of a chimney is merely the result of 

 accidental falling in of pellets from the rim, loosened perhaps by 

 atmospheric moisture. In some localities where the burrowing 

 crayfish abounds, there is a weather proverb to the effect that, 

 when the crayfish closes the opening of his chimney in dry 

 weather, there will be a rainfall within twenty-four hours." 



So far as I am aware, it is not known yet how the crayfish seals 

 up the orifice of his tower. Possibly it may do it by backing up 

 the burrow, and by turning around and about, manipulate the 

 moistened clay or mud into place by the use of its lateral tail-fins 

 and telson. That it is not due to the in-tumbling of the loose 

 pellets on top, there can be no doubt, for in the specimen at hand 

 the top of the sealed-up part is as thick as the sides (fully an 

 inch), and exactly resembles them, while the closed apex of the 

 passage inside is very smooth and carefully polished off. Why 

 it closes in its tower is hard to tell. It may be that finding the 

 orifice contracting too much, the cray seals up in order to pre- 

 vent the upper rim of the tower falling back into the burrow ; 

 it may be in order to shut out rain or rising water; it may be 

 to prevent attacks of enemies ; or it may be done while the 

 parent is laying her eggs at the bottom of the burrow. This all 

 requires further observations on the part of naturalists. It is 

 surely far easier for a crayfish to build a tower, even if two-fifths 

 of the pellets do roll down outside, than it would be for the 

 animal to carry all the pellets away from the mouth of its 

 burrow, and submit itself to capture by an enemy every time it 

 passed out with one. In short, it is the most convenient and 



