102 FAUNA OF MAYFIELD'S CAVE. 



nearest out-door relative, its parent species, the normal terranean 

 Asellus communis. Cambarus pellucidus has very degenerate eyes, is 

 entirely white, quite slender in body, and has long, delicate appendages, 

 and its sensory setae are longer than in ordinary crayfish. These are 

 familiar and typical cases. 



Some less extensive but very interesting modifications are those in 

 species found living within Mayfield's Cave and differing very slightly 

 from the same species when found living outside of caves in the im- 

 mediate neighborhood. A comparison of individuals of Cambarus bar- 

 toni living out-doors with those in Mayfield's Cave shows that those in 

 the cave have less pigment and that there are other structural differ- 

 ences. In the cave forms the antennae average 104.55 per cent the 

 length of the body, while in the outside forms the antennae are only 

 92.66 per cent of the length of the body. The series obtained from the 

 cave was not large, but the characters of having less pigment and 

 longer antennae were quite constant. A similar case is seen in Cran- 

 gonyx gracilis. Cave specimens of this species are without dark pig- 

 ment and reach a larger size than the same species living outside in 

 streams and pools near Bloomington. 



The species of Theridiidae present modifications both in the size of 

 the eyes and in the amount of pigment in direct proportion to the ex- 

 tent to which the species is subject to cave conditions. These modifi- 

 cations are discussed in detail and other modifications are noted in the 

 discussions of the different species. Packard (1888, 112, 120) noted 

 the same relation between the extent to which an animal lives within a 

 cave and its modification. Packard (1888, 120), Hamann (1896, 6), 

 Carpenter (1895, 29), Chilton (1894, 257, 258), and others have cited 

 other cases of animals living in caves possessing certain modifications 

 as compared with the same species outside of caves. 



There is very marked and striking uniformity in the modifications 

 of certain cave animals. Convergence is noted in a number of cases 

 among cave species. Eigenmann (1899) calls attention to a remarkable 

 case of convergence between Typhlichthys subterraneus and Troglichthys 

 rosas. He says, in part (1899, 281) : 



On the surface the specimens of Typhlichthys rosae very closely resemble Typh- 

 lichthys subterraneus from Mammoth Cave, differing slightly in the proportion and 

 in the pectoral and caudal fins. These fins are longer in rosas. It is, however, quite 

 evident from a study of their eyes that we have to deal here with a case of converg- 

 ence of two very distinct forms. The blind fish, Amblyopsis, may be left out of con- 

 sideration, since it is the only member of the family that possesses ventral fins. 

 Otherwise, it would be difficult to distinguish specimens of similar size of this species 

 from either subterraneus^pr rosse. 



