MEMOIRS OF THE NATIONAL ACADEMY OP SCIENCES. 123 



As regards Dr. Joseph's Cambarus stygius, based on au imperfect specimen from a cave in 

 Carniola, it appears that it is still uncertain, from a strictly systematic point of view, whether 

 it is a genuine Cambarus or Astacus, as Dr. Joseph does not say whether it comforms to the 

 genus Cambarus in the number and arrangement of the gills or »>ot. Joseph states that the hooks 

 spring from the second segment of the leg, but Professor Faxon thinks this is an error, since 

 in Cambarus these processes are always found on the third segment. Joseph apparently refers 

 it to the genus Cambarus from its close resemblance to G. pelhicidus, especially in the shape of 

 the body and the form of the non-facetted eyes. So good an observer as Joseph would scarcely 

 have made a mistake as to the position of the hooks, and this, at any rate, can scarcely be a char- 

 acter of importance. Systematists may carry trivial characteristics too far, and we do not see why 

 the profound modification of the eye, involving the absence of corneal facets, of rods and cones, 

 and of a genuine pigment, as well as the greater slenderness of the body and limbs, are not suf- 

 ficient characters to isolate these three blind species under the name Orconectes, especially since 

 there are no series of half or partially blind forms connecting the blind and normal species. On 

 the other hand, no one doubts but that the American species of Orconectes has been derived from 

 Cambarus, though the facts have not yet been discovered to show that the Carniolan species may 

 not have been derived from the European Astacus.* 



Finally, as regards all the eyeless genera in question, I do not see how we can in our system 

 put nature into a straight-jacket, and regard as simply of specific value the loss of eyes, sometimes 

 involving the total abolition of optic nerves and optic ganglia. It is a convenience not to lump 

 such forms with a mass of other species, where they will lose their individuality, but rather to 

 emphasize them by giving them distinct generic or at least subgeneric names. 



COMPENSATION FOR THE LOSS OF EYES OR EYE-SIOHT. 



As has been observed by some who have written upon cave animals, the atrophy of the eyes 

 and consequent loss of vision have been made up, in part at least, by a corresponding hypertrophy 

 of the organs of touch and smell. 



The more apparent anatomical modifications of the Arthropods consist in the greater slender- 

 ness of the body and the increased length and tenuity of the antenna) and limbs. 



In the planarian worms, however, there seems to be no other change than the loss of eyes 

 and a general albinism or degeneration of the pigment cells. 



Compensation by increase in the sense of touch. — It is in the Arthropods, whether Crustacea, 

 Arachnida, or insects, that we see the most marked change in the form of the body and its append- 

 ages. "When we compare the American species of Caecidotaea with'Asellus the body is seen to 

 be much attenuated, and the antennae much longer and slenderer, as*well as the legs. The genus 

 Crangonyx, according to Bate and Westwood, is nearest allied to a marine genus, Gammarella, 

 but the European species (C. sitbterraneus) have shorter antennae than the two species of Gamma- 

 rella figured in the " British Sessile-eyed Crustacea." On the other hand, the antenna?, of C. anten- 

 natus of Nick a jack Cave are longer than in any American or European species known to us. 



In the eyeless species of Niphargus the body is much slenderer than in the species of Gamma- 

 rus, and though the antennae are no longer, the last pair of uropoda are remarkably long and 

 slender. 



In the two species of blind crayfish the body is longer and slenderer than the normal Cambari; 

 the legs are slenderer, particularly the hands, while the antenuae are not longer in proportion to 

 the body than some species of Cambarus. Eyeless Myriopods, especially Pseudotreraia and Sco- 

 terpes, have longer antennae than in epigeau species. 



Coming to the bliud Arachnida, the bodies of the blind Ohernetidae tend to become much 

 longer, slenderer, and the eheliceres, as well as legs, much longer than is normal. This great 

 length of the legs, which may be regarded as tactile organs, enabling them to be used for sound- 

 ing objects, is most marked in Phalangpdes armata when compared with the Coloradan P. 

 robusta. 



" It may be observed that in his "Etades" on Phyllopodes, in referring to Joseph's eyeless cave Branchipus pellnci- 

 t!u8, M. Eug. Simon remarks: "Espece aveugle qui deviendra sans donte le type d'un genre special." 



