128 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



In their native pools and in the aquarium when disturbed they do not strike the bottom or sides of their surround- 

 ings, but seem to have a sense of resistance (if the term is pardonable) which protects them. I can only regret that 

 I have not examined those recently caught to ascertain the nature of their food. I never observed any excrement 

 voided by them. 



Though the ears of Amblyopsis are said by Wyman to be "largely developed" and the oto- 

 lite of the vestibule "quite large wheu compared with that of a Leuciscus of about the same 

 dimensions as the blind-fish," yet according to Dr. Sloan's statement this fish is not sensitive 

 to sounds. As he is a good observer, and has kept these fish in a large, spacious tank for 

 twenty months, where I have seen them, his observations must be relied upon. Dr. Wyman, 

 however, remarks: "It is said that the blind-fishes are acutely sensitive to sounds as well as to 

 undulations produced by other causes in the water."* It is evident that further experiments on 

 living blind fishes as well as more extended anatomical investigations are needed to settle the 

 question whether the fish are generally seusitive to sound. It may be said in this connection that 

 so far as is known most of the cave Arthropods, at least the insects, are not provided with organs 

 of hearing, the olfactory being the prominent sense in eyeless insects. On examining the audi- 

 tory sacs of Orconectes liamulatus and comparing them with those of an undetermined species of 

 Cambarus with normal eyes, they are about one-third smaller, while the auditory setae are remark- 

 ably small, being only one-third as long as in the Cambarus with normal eyes, while the hairs are 

 only about as long as the seta is thick ; whereas iu the normally eyed Cambarus the hairs are 

 very long, being from six to eight times as long as the seta is thick. Hence we infer that the ear of 

 Orconectes is degenerate and the sense of hearing nearly if not quite obsolete. The ear of 0. pel- 

 lucidus, from a cave in Indiana, is also much reduced in size, being about as large as that of 

 0. hamulatusj (Compare PI. XXI, figs. 4, 5, and 6.) 



In the inole,f which has minute eyes, the sense of hearing, and probably of touch, compensates 

 for the loss of eye-sight, which is of no advantage to it in its subterranean life. 



In the Spalax of eastern Europe and western Asia, a mammal not a troglodyte, but living a 

 subterranean life like a mole, we have, according to Dr. Duchamp, an interesting case of compen- 

 sation for the loss of vision. The eyes are so atrophied, being covered by the skin, that this 

 rodent is said to be practically blind, but as a compensation the sense of touch residing in the 

 hairs situated about the mouth is exalted, while the auditory passage and internal ear are nor- 

 mally developed, though the outer ear is wantiug.§ 



* If these Amblyopses be not alarmed, they come to the surface to feed and swim in full sight, like white aquatic 

 ghosts. They are theu easily taken by the baud or net if perfect silence is preserved, for they are unconscious of 

 the presence of an enemy except through the medium of hearing. This sense is, however, evidently very acute, for 

 at any noise they turn suddenly downward and hide beneath stones, etc., on the bottom (Cope, Amer. Naturalist, 

 vi, July 18, 1872). 



t In a Cambarus 50 mm long from the tip of the rostrum to the end of the telson, with normal eyes, the basal 

 joint of the first antenna is 4.5 mm , while the length of the ear capsule is 2 mm ; in 0. hamulatus, 45 mm in length, the 

 basal joint is 2.8 mm in length, and the length of the ear capsule is 1.4 m,n long; in an 0. pellucidus from Indiana 40 mm 

 long the basal joint is 2.2 mm long and the auditory sac about 1.5 mm in length. It thus appears that the basal joints 

 or scape of the first antenuae, as well as the ears, are much smaller in proportion in Orconectes than in the Cambarus 

 with normal eyes. 



i Savi has described "une vari6te' coinpleternent aveugle," Duchamp, I. c. "The eyes of moles and of some bur- 

 rowing rodents are rudimentary in size, and in some cases are quite covered up by skin and fur. This state of the 

 eyes is probably due to gradual reduction from disuse, but aided perhaps by natural selection. In South America a 

 burrowing rodent, the tuco-tuco or cteuomys, is even more subterranean in its habits than the mole; and I was 

 assured by a Spaniard who had often caught them that they were frequently blind ; one which I kept alive was cer- 

 tainly in this condition, the cause, as appeared on dissection, having been inflammation of the nictitating membrane. 

 As frequent inflammation of the eyes must be injurious to any animal, and as eyes are certainly not necessary to ani- 

 mals having subterranean habits, a reduction in their size, with the adhesion of the eyelids and growth of fur over 

 them, might in such case be an advantage; and, if so, natural selection would constantly aid the effects of disuse" 

 (Darwin's Origin of Species). Also compare foot-note on p. — . 



§ Mais si 1'cb'lI du Spalax, cach6 sous la peau, est incapable de remplir ses fonctious, deux autres sens, l'ouie et 

 le tact, largement d6velopp6s, viennent supplier a l'absence du premier, disposition d'autant plus int^ressante qu'elle 

 est constaute chez toutes les especes de la faune souterraine. 



Tous ces poils raides qui he"rissent les bourrelets eephaliques et la region circumbuccale, probablement aussi 

 ceux que l'on rencontre a la p6riph6rie des pattes ant6rieures, sont autant d'organes tactiles qui, multipliant les sen- 

 sations, ne permettent a aucun corps de passer inapercu. 



Hceil demeurant sans exerciee s'est atrophi6, le pavilion auriculaire qui genait l'animal dans l'inte"rieur de ses 



