94 FAUNA OF MAYFIELD'S CAVE. 



exists between cave species and their near relatives outside could hardly 

 be more striking. 



This brings us to another point the persistence of certain habits in 

 cave species habits which in their outdoor relatives are absolutely 

 essential to self-preservation, but which in the cave species are entirely 

 useless. Packard (1890, 394) calls attention to this fact: 



Although scarcely necessary in its changed environment, where there are no 

 hydrographic changes, no winter and summer, and few enemies to contend with, the 

 most aberrant form, the completely eyeless form Anthrobia of Mammoth Cave, still 

 spins a silk cocoon around its eggs; while in Weyer's Cave Nesticus pellucidus Emerton 

 spins a cocoon for its eggs; and either this species or its fellow troglodyte Linyphia 

 incerta Emerton, or both species, spin a weak, irregular web, consisting of a few 

 threads. Is not this a useless habit, the simple survival of ancestral traits? 



W. P. Hay (1902, 436), regarding this point, says: 



I would regard the habit of living under stones of Cambarus hamulaius and 

 Csecidotea richardsonse as a primitive instinct to which the animals cling in spite of 

 the fact that it is useless. 



Eigenmann (1899, 477) says: 



Typhlichthys, living in total darkness, has retained the habit of staying under 

 floating boards, sticks, and stones. Miss Hoppin noticed that Troglichthys swims with 

 its back to the side of the aquarium, and I have repeatedly noted the same in the young 

 of Amblyopsis up to 50 mm. and the still younger Amblyopsis frequently hides under 

 rocks. 



Many cave animals habitually live under stones or debris. This is 

 the habit of the true cave spiders, of the cave Staphylinidae, and to 

 some extent of the thysanuran Sinella and of Ceuthophilus. The prev- 

 alence of this habit of concealment could scarcely be over-emphasized. 

 Small indeed would be one's collections, except for a few of the Diptera 

 and the Ceuthophilus, did he not hunt out these places of concealment. 

 One could as successfully collect in the woods in winter without looking 

 under the bark of trees, under logs, and other such places as collect in 

 caves without searching in cracks of the rock and under pieces of stone 

 and other debris. It is unnecessary for these animals to take to such a 

 habit to escape enemies, cave air is generally moist, and there is no 

 sunlight to avoid, hence the habit appears to serve no useful purpose. 

 The cave spiders spin small webs, which, certainly in the case of Phanetta 

 subterranea and Erigone infernalis, are entirely useless to catch prey or, 

 as near as can be determined, to serve any useful purpose whatsoever. 

 Phanetta subterranea spins a compact disk-shaped cocoon when the need 

 for a cocoon to protect the eggs or young is not apparent. These are 

 ancestral habits which, though once useful, are no longer so; yet they 

 persist in these troglodytes with a remarkable tenacity. 



