404 FISHES 



seems, therefore, that the pink colour is not due merely to the 

 loss of pigment but is caused by a positive development of 

 blood-vessels in the skin, which doubtless perform the function 

 of cutaneous respiration ; the supply of oxygen in the holes in 

 which the fish lives must be considerably reduced, since there 

 is no free movement of water through them, and thus we can 

 understand that it is advantageous or even necessary to the 

 fish that the ordinary respiration of the gills should be supple- 

 mented by absorption of oxygen through the skin. The cave- 

 fish Amblyopsis lives in running water in which there is no 

 dearth of oxygen, and accordingly, although its pigment has 

 disappeared in consequence of the absence of light, its skin is 

 not specially vascular and its colour is not pink but white. The 

 cutaneous respiration of Typhlogobius explains its power of 

 living in foul water in captivity. 



In all the gobies the sensory tubes of the lateral line and 

 head are wanting and the sensory organs of the head are on 

 the free surface of the skin. It has been suggested that in 

 Typhlogobius the reduction of the eyes is compensated by the 

 higher development of these dermal sense-organs, but W. E. 

 Ritter found that such organs were less numerous in the blind 

 species than in more normal forms. In Typhlogobius there is 

 a series of sensory papillae parallel to the lower jaw, another 

 series on the upper jaw and another on the operculum, but on 

 the sides of the body sense-organs are entirely wanting ; in the 

 species possessing the sense of sight these series on the head are 

 present and there are also others scattered on the head and 

 numerous transverse series on the sides of the body. 



A very extraordinary condition of the eyes occurs in Sty lop h- 

 thalmus paradoxus, a deep-sea fish of the Indian Ocean : the 

 organs are at the ends of long slender stalks projecting from 

 the sides of the head. The stalks become shorter in the adult 

 fish. 



