MEMOIRS OF TDE NATIONAL ACADEMY OF SCIENCES. 47 



sleiider legs and no eyes, in reality differ more from the other species of Obisium than does the 

 generally-accepted genus Chthonius. As we have attempted to show however, contrary to Hagen's 

 opinion, the American C.packardii is not a true Blothrus ; it could not properly be separated from 

 C. ccecus. They both agree in the short, thick, conical third joint of the pedipalps. 



It may be interesting in this connection to learn something of the habits of the species of tbe 

 two genera Obisium aud Chthonius. As almost nothing is known of the habits of our American 

 species, we are obliged to compile the following account from M. Simon's excellent work. 



The species of Obisium live in moss and vegetable detritus; they are very agile, and run back- 

 wards easily. Of seventeen species three (Blothrus) have no eyes and inhabit caves; these three 

 have been already referred to byname. Of fourteen French species with eyes, one only (0. cavcr- 

 narum) has " very small pnnctiform eyes." It is a cave-dweller. Of the fourteen species, only one 

 other lives in caves; this is 0. lucifugum. In this species the eyes are <; very small." All the 

 other species have either four or two eyes. We here see a very direct connection between cave- 

 life and the eyeless forms in the species of southern and central Europe. 



Turniug to the genus Chthonius, there are seven French species described by Simon. He 

 says that u the Chthouii also seek dark and damp places; several are peculiar to grottoes, and 

 the ordinary species are sometimes met with in wood-piles and caves. Thus at Troyes M. J. Ray 

 has observed in caves three species of Chthonius (rayi, orthodactylus, tetrachelatus), where they run 

 with agility on the walls, and escape by hiding in the little fissures, in which they shoot forward 

 as previously described." 



Of the seven species of Chthonius enumerated by Simon one (G.-cephalotes) has no eyes ; it lives 

 in caves. In C. microphthalmus the eyes are very small ; it also usually occurs in caves. Thus 

 the majority of the species occur in caves; three of them permanently so. It will also be seen 

 that there is an obvious relation between those which are totally blind and live in caves; i. e., 

 those without eyes inhabit caves exclusively, those with very small eyes are found partly or mostly 

 in caves, and those with perfect eyes are not cave-dwellers. The relations of cause aud effect in 

 the blind species of this family are, then, very marked, the adaptation to life in partial or total 

 darkness involving the disuse and consequent atrophy of the organs of sight. It is so also with 

 the North American species. 



To return to the American cave species : It appears that in inhabitants of even one cave 

 (Mammoth) there are individuals of Chthonius ■paclcardii existing, as regards the eyes, in three 

 conditions, though all must be in total darkness. (I) Some have two eyes, with the cornea as 

 usual; (2) some have no cornea, but the silvery dot indicating the retina is retained; while iu 

 others all traces of the eyes have disappeared. On the other hand, in those individuals existing in 

 Salt Cave (a small cave not wholly dark) the two eyes are distinct. These facts would indicate 

 that the Mammoth Cave examples must be the descendants of some out-of-door species, to which 

 the Salt Cave individuals are nearest allied. Moreover, the difference between the eyed and 

 eyeless forms are apparently individual rather than varietal.* The presence or absence of eyes 

 in this case are not generic characters. The cave forms retain the generic characters of out-of 

 door species of Chthonius, both American and European. The characters iu which individual vari- 

 ation of C.paclcardii occurs are apparently the parts of the eyes alone. This loss of eyes, partial 

 or total, seems to us to be the result of the direct influence of the surroundings upon the organism. 

 When we take into account both the European and American species as a whole (0. ccecus, with 

 its stout body, being an as yet inexplicable exception), the eyeless species have, besides the loss 

 of eyes, very slender bodies and remarkably attenuated pedipalps and legs, especially the hinder 

 pair. We do not think that natural selection can in such a case as this be regarded as an efficient 

 cause in producing the cave forms. The eyes are useless in total darkness ; hence from disuse 

 they gradually, after a few generations, disappear. On the other hand, the limbs tend to grow 

 longer, to perhaps exert a tactile sense; and this trait, being favorable to the species, is gradually 

 further developed, until it becomes fixed in the organism by heredity. The result is that all the 



* Those from the Rotunda have eyes (Hubbard); those from the Labyrinth had piyment-spots or were totally 

 blind. The Rotunda in much nearer the mouth of the cave than the Labyrinth (see man); hence tho eyed forms 

 may have been more lately introduced into the care. Further research should be made iu this direction. Dr. Ha- 

 gen's specimens were mixed up, part from Mammoth and part from Long Cave. 



