536 LAND ANIMALS 



moth Cave. 35 Some cave forms have a definite breeding season; Lar- 

 tetia lays eggs in February and Cambarus breeds in the fall. 



The presence or absence of air currents in caves seems to be of im- 

 portance to the development of their peculiar population, as air cur- 

 rents tend to upset the uniformity of humidity and of temperature. 

 Caves in which air currents are developed do not have a true cave 

 fauna. 36 



Isolation in caves. — Isolation is an important factor in the devel- 

 opment of the cave faunae, for it is more effective even than on islands 

 in separating small areas. Even though there may be more connections 

 between caves in limestone regions than are apparent, such systems of 

 caves are well isolated, and such isolation explains their faunistic 

 peculiarity. The cave faunae of Moravia exhibit a great preponder- 

 ance of springtails and mites, which together make up more than four- 

 fifths of the fauna, while the caves of the Karst are characterized by 

 pseudoscorpions, blind beetles, and the olm. The cave fauna of the 

 Swabian Alps, as contrasted with the French Jura, is characterized by 

 the development of the genus Lartetia. 



The similarities between the cave faunae of widely separate regions 

 are attributable to the fact that only members of certain groups are 

 able to adapt themselves to cave conditions, and that such adaptation 

 produces parallel structure and appearance. 



The frequent appearance of endemic forms confined to single caves 

 or cave systems has already been discussed (p. 91). It is evident 

 that this is not merely an appearance of rarity due to inadequate 

 knowledge but represents an extreme of range and habitat restriction. 



The isolation in caves, combined with the selection of the entrants 

 exercised by the peculiar conditions, removes many cave animals from 

 the stress of the terrestrial struggle for existence. Snails are safe from 

 their enemies ; beetles have none except spiders and mites ; amphipods 

 have enemies only where fishes and salamanders exist. Thus, in addi- 

 tion to animals with close relatives above ground, cave faunae exhibit 

 a considerable number of relicts, whose terrestrial ancestors are ex- 

 tinct. Such relicts are the snails of the genus Lartetia in the Swabian 

 Alps.* Two representatives of the primitive crustacean Bathynella are 

 found in caves and springs in central Europe. These belong to the 

 Palaeozoic group of crustaceans, Syncarida, which have representatives 

 in surface waters in Australia and Tasmania. 37 The olm is such a relict. 

 Another group of relicts is composed of forms with marine relatives, 



* Also Meledella werneri, Pholeoteras euthrix, Phygas colasi, and Spelaeo- 

 concha in the south Dalmatian caves. 



