SUBTERRANEAN ANIMAL LIFE 535 



light and shows superior discrimination as regards food.-'*' In Vire's 

 experiments with Gammarus, 27 a notable hypertrophy of the chemical 

 sense organs appeared after a few months below ground. Two hyaline 

 bulbs occur on each antenna of a blind gammarid from a cave in 

 Montenegro, instead of the single one of the brook amphipod. 28 Ob- 

 servation shows that cave animals move with as much certainty as if 

 they could see. Springtails, for example, often leap at the right moment 

 to escape from attacking mites. 29 



Humidity and temperature. — The constant moisture of their 

 habitat, which removes all danger of drying out, is of especial impor- 

 tance to cave animals. In Algeria entirely dry caves lack animals while 

 moist ones are well inhabited. The skin of cave insects and their larvae 

 is much thinner than in their epigean relatives. 30 The snails of caves 

 have thin shells, as in humid regions. The cave salamander, Hydro- 

 mantes fuscus, of southern Europe can exist in the humid air of caves 

 and crevices in summer, while its fellows outside of caves are forced 

 to find hiding places in the ground. Typhlotriton spelaeus in North 

 America is at home both in and out of the water. 31 Small drip-pools 

 in caves are inhabited by amphipods, from which it may be concluded 

 that they are able to pass from pool to pool without drying. The re- 

 markable air-breathing turbellarian Geopaludicola, secured in central 

 Dalmatia, differs in structure from all other land planarians and re- 

 sembles the aquatic triclads. 32 This appears to be a genuine example 

 of change from aquatic to air-breathing life on the part of this turbel- 

 larian, doubtless after taking up residence in caves, where the humid 

 air removes the danger of drying in the course of the transformation. 

 Cave animals sometimes retain vestigial habits which have only his- 

 torical significance. Thus land isopods are positively thigmotropic and, 

 by living under stones, escape from light to which they are negative 

 and from many epigean enemies, and also find optimal moisture rela- 

 tions. The habit is retained by cave dwellers although the thigmotropic 

 reaction has little, and at times probably none, of its epigean value. 



Caves are well suited to stenothermal animals, and investigation 

 has shown that many cave animals are more than usually sensitive to 

 raised temperatures. The turbellarian, Dendrocoelum cavaticum, dis- 

 integrates when one attempts to transport it on a warm day in a flask 

 of water, 33 and Niphargus dies at 20°, while Gammarus can withstand 

 a further rise of 10°. 34 Uniformity of temperature has the same effect 

 as in the tropical rain-forest in that periodicity of breeding season dis- 

 appears in many forms. Among the Cuban blind cave fishes, Lucifuga 

 and Stygicola, pregnant females are to be found throughout the year, 35 

 and the same is true of the similarly viviparous Amblyopsis of Mam- 



