some Freshwater AmpJiipods. 237 



mentioned and brino' it in some respects near to Gammarus 

 and in others to Nipharr/us. 



According to de Vismes Kane, Bathijonyx was obtained 

 from a depth of from 130 to 150 feet in Lough Mask. From 

 tlie general liabitus of its bodj and most of the details of its 

 organization it may be regarded as a degenerate form, a 

 conception which is strongly supported by the sense-organs, 

 especially the eyes. All the above-mentioned cuticuiar 

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

 in all species of Gaiumarus living in ordinary fresh waters, 

 but in much greater number and development than in Bathy. 

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

 corresponding to that of the eyes, and cannot therefor-e be 

 considered as compensatory organs. The ancestors of Bathij- 

 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. There is no reason for sup- 

 ])osing that these crustaceans reached the lake in the water 

 from the springs ; their organization strengthens us rather 

 in the opinion that the progenitors are to be sought perliaps 

 only in a species of Cranyonyx or G ammarus which gradually 

 adapted themselves to life at the bottom of Lough Mask. 

 Altiiough species of Crangonyx possessing eyes are known, 

 among which especially C. reciirvus, according to Grube, 

 lives in Lake Vrana, on the island of Cherso, 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 subterranean 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. !So far as the 

 freshwater Ampliipoda 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'i JS^ iphargus puteanus were 

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

 the eyes are situated in such a form as the common 

 Gamm,arus. 



* From an interesting paper by M. Grocliowski (ii) I learn that he 

 and Professor B. Dybowski found in 1895 a large number of C. recurvus 

 in the lake mentioned. A special account of this species therefore may 

 be expected. 



