530 LAND ANIMALS 



unknown. Dendrocoelum subteiraneum is also reckoned as one of the 

 older entrants. Data for valid conclusions of this nature are inadequate. 



The cave environment. — Deep within the caves the habitat con- 

 ditions are remarkably uniform. Uniform darkness, uniform high hu- 

 midity, temperature with slight variation, near the annual mean of the 

 locality, and almost complete absence of air currents, characterize 

 the cave environment. Rain and snow and heat are unknown in caves. 



The absence of light in the subterranean spaces is the most impor- 

 tant feature of this environment to its animal population. It is even 

 more complete than in the abyssal ocean, where light-producing ani- 

 mals exist in considerable numbers. Animals in the depths of fresh- 

 water lakes are not so completely cut off from light, as they are able to 

 swim up to the lighted layers. The effect of total darkness is manifest 

 in various ways. 



The absence of green plants is fundamentally important. From this 

 it follows that the food of cave animals must come from without, 

 except as the roots of surface plants may reach these depths. This food 

 supply is of varied character. An important element is plant debris, 

 wood, leaves, etc., on which molds and other fungi are able to grow. 

 More than 10 species of such plants without chlorophyll have been 

 found in the Karst caves. These support fungus-eating beetles* and 

 snails. Caves with a down slope at the entrance are in consequence 

 much richer in life than those in which the entrance rises from the 

 opening, since the entry of debris is thus facilitated. Flowing water 

 also carries in food materials. The bat guano, sometimes present in 

 enormous amounts, affords a food supply to springtails and mites. 

 Finally, dissolved and colloidal food substances of plant origin are 

 carried in by the ground water. Springtailsf and mites occur in incred- 

 ible numbers in the recently wholly closed Sosuvka Cave in Moravia. 11 

 Many stalactites and stalagmites are literally covered with these 

 animals. The springtails gather at the moist places to feed on the col- 

 loidal substances carried in by the seepage, especially around the 

 cup-shaped depressions on the stalagmites. 



The size and number of inhabitants afford a measure of the amount 

 of food available in a cave. The food supply is in general small, and 

 cave life is correspondingly scanty and made up of small forms. The 

 cave snails, especially the plant feeders, are mostly tiny, measuring 

 only a few millimeters in length. Only a few predaceous pulmonates in 

 the Balkan caves can be said to reach a moderate size. 12 Springtails 



* The so-called cave-silphids, Adelops, Orycus, Lcptoderes, etc. 

 t Dicyrtoma, Hctcromurus, and Anurophorus. 



