CAMBARUS. 73 



of the ground the excavation exhibits a gradual slope, in direction more or 

 less undulating lor a distance from five to ten inches, when it becomes verti- 

 cal l'or six or eight inches, and then terminates in a sudden bottle-shaped 

 enlargement, in which the animal is found. The bottom of the burrow 

 having no subterraneous communication, no other issue except towards the 

 surface, it is entirely isolated from its neighbors, and leaves no chance for 

 escape to its inhabitant. The same burrow may have several external holes 

 connected with it, several inclined channels, which, however, meet at the 

 depth where it becomes vertical. We found constantly the cavity full of 

 water, but this was in March and April. The bottom, for several inches, was 

 filled with soft and pulpy mud. 



"There are other instances of burrows somewhat more complex. Their 

 direction may be oblique throughout their whole extent, and composed of 

 a scries of chambers or ovoid enlargements succeeding each other at short 

 intervals. Sometimes, also, and connected with one of the chambers, a nar- 

 row and nearly vertical tubuliform channel extends downwards to a much 

 greater depth, and appears to us as a retreat either during the cold win- 

 ters or else during the dryness of the summer, when water is low. That 

 it is not for the mere purpose of escaping pursuit, we infer from the fact 

 that we repeatedly caught the animals in the chambers above, where they 

 remained quietly, instead of attempting to disappear into the apartments 

 below 



" In the spring, and we are told in the fall also, the burrowing craw- 

 fish builds over the holes of its burrow a chimney of the maximum height 

 of one foot, but most generally lower. The chimney, circularly pyramidal in 

 shape, is constructed of lumps of mud, varying in size, irregularly rolled up, 

 and piled up one upon each other, and intimately cemented together. Its 

 exterior has a rough and irregular appearance ; whilst the interior is smooth 

 and as uniform as the subterraneous channel, having the same diameter as 

 the latter 



" The animal works during night. How the work is performed has not 



}^et been ascertained by actual observations On an examination of 



these chimneys, we detected ihe imprints of the second and third pair of 

 claws, which indicate, evidently, that the parcels of mud. once brought to the 



surface are arranged and fixed in their definitive place by means of 



these organs. 



•■ When the work has thus been carried on towards completion, the last 



10 



