some Freshwater Amjihipodn. 237 



mentioned and brino^ it in some respects necar to Gammarus 

 and in others to Niphargus. 



AccordinfT to de Vi.sines Kane, Bath/onyx was obtained 

 from a depth of from 130 to 150 feet in Louc^h Mask. From 

 the general habitus of its body and most of the details of its 

 organization it may be regarded as a degenerate form, a 

 conce])tion which is strongly supported by the sense-organs, 

 es])ecially the eyes. All the above-mentioned cuticular 

 sense-organs, as the sensory brushes and capsules, are present 

 in all species of Gammarus living in ordinary fresh waters, 

 but in much greater number and development than in Bathy. 

 onyx, Mdiere they are subject in both directions to a reduction 

 corresponding to that oif the eyes, and cannot therefore be 

 considered as compensatory organs. The ancestors of Bathy- 

 onyx evidently possessed the same sense-organs as, for 

 example, the common Gammarus, and in the same number 

 and development, but they degenerated in the course of time 

 in the depths of Lough Mask. Tliere is no reason for sup- 

 ])Osing that these crustaceans readied the lake in the water 

 from the springs ; their organization strengthens us rather 

 in the opinion that the progenitors are to be sought perhaps 

 only in a species of Crangonyx or Gammarus whicli gradually 

 adapted themselves to life at the bottom of Lougli Mask. 

 Although species of Crangonyx possessing eyes are known, 

 among which especially C. recurvus, according to Grube, 

 lives in Lake Vrana, on the island of Oherso, unfortunately 

 its organization has not been hitherto carefully studied *. 

 From what has been said it appears that we must attach the 

 greatest importance to the eyes. 



The gradual adaptation to life in the darkness of deep 

 lakes and sul)terranean waters generally produces the result 

 that the organs of sight are gradually, not suddenly, reduced, 

 until at length the animal appears quite eyeless, and trans- 

 mits its blindness to the following generations. iSo far as the 

 freshwater Aniphipoda are concerned, we now know a series 

 of cases in which we must conclude that eyes were formerly 

 present. Reference has often been made to the observation 

 of Leydig that certain individuals o( jyijJiaryua puleanus were 

 provided with eye-pigment just in that part of the head where 

 the eyes arc situated in such a form as the common 

 Gammarus. 



* From an interesting paper by M. Grochowski (ii) T learn that be 

 and Professor B. Uybowski loiuid in 1895 a larj<;e number of C. recurvus 

 in tbe lake mentioned. A special account of this species therelure may 

 be expected. 



