394 THE POPULAR SCIENCE MONTHLY. 



tail elsewhere, illustrate clearly the theory that certain subter- 

 ranean forms, living deep in the soil, under stones in the cave 

 regions of both hemispheres, especially in France and Austria, 

 have been carried into caves, have survived the loss of out-of-door 

 conditions, becoming adapted to the new and strange environment, 

 losing their eyes totally or in part from disuse of those organs, and 

 have bred true to the new specific characters thus established, 

 and are now as unchangeable as the physical conditions in which 

 they live. 



The cave spiders in all important respects exemplify the same 

 rule. They belong to, or are closely allied to, genera rich in 

 species in the cavernous regions they inhabit, and which live in 

 dark places. Although scarcely necessary in its changed environ- 

 ment, where there are no hydrographic changes, no winter and 

 summer, and few enemies to contend with, the most aberrant 

 form, the completely eyeless Anthrobia of Mammoth Cave, still 

 spins a silk cocoon around its eggs ; while in Weyer's Cave Nes- 

 ticus pellidus 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, a simple survival of ancestral traits ? 



It was noticed that the number of individuals of different 

 species was greater in the smaller shallower caves, such as the 

 Weyer and Carter Caverns ; each of these groups of caves has 

 three species, while in Mammoth Cave there is but one, and the 

 individuals are less common. Moreover, all are darker than An- 

 throbia, all have eyes, and the number of eyes is variable. These 

 facts show that Anthrobia and the eyed forms have originated 

 from species living in partial darkness at or near the mouths of 

 the caverns. In Mr. Emerton's description of Linyphia incerta 

 it will be seen how variable are the number of eyes. From this 

 it may be inferred that the specific characters of this form, as re- 

 gards the eyes at least, have not been firmly established, and 

 hence it has only recently become a true troglodyte. 



In the foregoing examples we have as yet not discovered in 

 this country any connecting links between the eyed and blind or 

 eyeless species of cave animals. But in a series of specimens of a 

 cave myriapod, Pseudotremia cavernarum, which is abundant in 

 the Wyandotte and Carter Caves, we have what we regard as 

 good, if not complete, evidence that this cave form has directly 

 originated from a common and widely distributed out-of-door 

 form. The cave Pseudotremia has black eyes, composed of from 

 twelve to fifteen facets arranged in a triangular area ; of one hun- 

 dred and fifty specimens examined none were found to be eyeless. 

 In a large cave like "Wyandotte there is little variation in this 

 species as regards size, proportion, or color (being white with a 



