SUBTERRANEAN ANIMAL LIFE 529 



mals, however, are arthropods, including aquatic crustaceans and ter- 

 restrial insects and arachnids. Besides entomostracans, cave crusta- 

 ceans include amphipods, isopods, and decapods. Among insects the 

 springtails predominate (Fig. 132) together with beetles, the other 

 orders being only sparingly represented. Among arachnids, mites and 

 true spiders are most numerous with pseudoscorpions and phalangicls 

 also present. Vertebrates are represented by fishes and salamanders. 

 Coelenterates, bryozoans, tardigrades and lamellibranchs are thus far 

 unknown in caves; insects which depend on green plants for food are 

 excluded, and reptiles, birds, and mammals have not developed true 

 cave forms although snakes are occasionally found and Steatornis al- 

 most qualifies as a cave bird. 



The cave fauna originated on the surface, and many forms were 

 already adapted to moist, cool, and dark habitat conditions before 

 entering caves. All triclad turbellarians are negatively phototropic, and 

 live beneath stones or in similarly dark places during the day. The 

 terrestrial beetles, Trechus, live concealed under stones and in similar 

 places, especially in forests in the mountains; Jeannel says, in his 

 monograph on the distribution of American species, that, in entering 

 caves, they have not essentially changed their habitat. 7 Springtails 

 and mites are everywhere photonegative, and are often blind even 

 when not subterranean in habits. The fishes of the family Amblyopsidae 

 (to which the cave fishes belong), which live in surface waters, are 

 negative to light and conceal themselves under stones. 8 The entry into 

 the cave habitat was made in various ways. Some forms were carried 

 in by water; others, working their way against the current, found caves 

 at the source. Terrestrial animals wandered in at cave mouths, but also 

 entered by way of cracks and rock clefts. The cave of Sosiivka in 

 Moravia, which was until recently without an opening, contains only 

 9 species, 5 springtails and 4 mites, all extremely minute forms. Open 

 caves in the same region have a richer fauna; the Sloup cave harbors 

 more than 50 species, and the cave of Vypustek, about 30. 9 



From the extent of their transformation, conclusions have been 

 attempted as to the length of time elapsed since the entry of certain 

 animals into caves. Thus Komarek 10 distinguishes younger and older 

 cave forms among planarians. The younger, PL anophthalma and PI. 

 montenegrina, are races of Planaria alpina, which is a stenothermal 

 animal of cold habitat and could have reached the Balkan Peninsula 

 only during the glacial period, so that the date of entry of its deriv- 

 atives into caves is placed as post-glacial. Sorocelopsis decemoculata, 

 and the "land triclad" Geopaludicola absoloni, seem to have been 

 longer in the cave habitat, as planarians of their type are otherwise 



