THE GBAYFISH 131 



some species prefer cool mountain streams and others muddy- 

 pools, while certain species, both in Europe and America, are 

 found in brackish as well as fresh water. Indeed, the Euro- 

 pean Astacus fluviatilus is said to be frequently caught off the 

 Livonian coast, even some distance out at sea. Individuals 

 of an American species have been taken from a mineral spring 

 impregnated mth sulphur and magnesia at a temperature of 

 70° F. (21° C), while several kinds of the American "bur- 

 rowing " or " chimney "-forming species have been found 

 in meadows and clay bottoms, often at great distances from 

 streams. Certain species that are blind inhabit caves only. 

 In England, according to Huxley, " in granite districts, and 

 others in which the soil yields little or no calcareous matters 

 to the water which flows over it, crayfishes do not occur. 

 They are intolerant of great heat or of much sunshine ; hence 

 they are most abundant in those parts of rivers which flow 

 east and west, and thus jdeld the most shade from the midday 

 sun." 



There are two great groups of subfamilies of crayfishes. 

 One, restricted to the Northern Hemisphere, is found in 

 Europe, Asia, and North America. The other is found in the 

 Southern Hemisphere, in Australia, Tasmania, New Zealand, 

 Fiji Islands, Madagascar, and South America. No craj'fishes 

 have been found on the continent of Africa or in the rivers of 

 northern Asia that flow into the Arctic Ocean, or in those of 

 southern Asia. These Asiatic rivers are populated by fluviatile 

 crabs, to which the crayfishes of the region have probably 

 succumbed. All the islands now inhabited by crayfishes, such 

 as England and Japan (excepting Cuba), were prol^ably once 

 connected with the mainland (Fig. 130). 



The northern subfamily of crayfishes contains, according 



