HIGHER CRUSTACEANS (MALACOSTRACA) 837 



chimneys have attracted much attention, and the idea has been 

 advanced that the chimneys are constructed by the crayfish for a 

 certain definite (useful) purpose. But recent investigations seem to 

 point to the conclusion that the regular shape of the chimneys, 

 when present, is accidental, and the mud piles are nothing but the 

 natural product of the burrowing, disposed of in the most con- 

 venient way (around the mouth of the hole) . The burrows them- 

 selves are rather irregular, more or less complex, and consist of 

 simple tunnels, often branching, and one or more pockets, or widen- 

 ings of the tunnel. They go down into the ground from one to 

 several feet, but always deep enough as to contain ground-water, at 

 least at the bottom. 



Burrowing species are found chiefly in the subgenus Bartonius, 

 and form a very well defined morphological group, and it is just 

 this group of this subgenus, which has spread out from the original 

 territory (the mountains), and has descended into the plains. On 

 the western and southwestern plains is found another group of 

 burrowers which belong to the subgenus Cambarus. 



Another special ecological group should not be forgotten. These 

 are the cave species. With the exception of the Mysidacea, all 

 our fresh-water Malacostraca have developed certain forms which 

 are adapted to the life in subterranean waters, and live in caves, 

 springs, artesian wells, etc. This peculiar habitat has affected 

 their structure greatly, and the most important and interesting 

 feature is the loss of the eyes. Some of these forms are entirely 

 blind, having lost the visual elements of the eyes (cornea and pig- 

 ment), while in others the reduction is only partial. 



Among the Isopods, the only North American fresh-water form, 

 belonging to the Cirolanidae, is a blind subterranean form (Giro- 

 lanides texensis, Fig. 1304). Of the Asellidae, some live in caves and 

 have suffered the loss of the eyes. This is especially true of the 

 genus Caecidotea, the species of which have been found in caves of 

 Virginia, Georgia, Tennessee, Kentucky, Indiana, Illinois, and in 

 subterranean waters in Texas. Mancasellus, which possesses eyes, 

 has often been found in caves or in streams issuing from caves ; it also 

 lives in the Great Lakes. 



