14 



bedded in muscles, and quite covered mth the external skin, is 

 not easily detected. True eyeless fishes have been hitherto found 

 only at great ocean depths, and we are indebted for our knowledge 

 of them to the "Challenger" expedition. Many of these eyeless 

 fishes have on the head peculiar and sometimes very large organs 

 which have displaced the eyes. These may, according to Dr. 

 Giinther, be strongly developed phosphorescent organs; while 

 the non-bHnd fishes of the deep ocean have exceptionally large 

 eyes, which seem fitted to absorb pale phosphoric light. Sir 

 Wyville Thomson thinks these large eyes have become exagge- 

 rated, to enable the fishes to catch the feeble rays of light coming 

 from above; although he acknowledges that, so far as he can 

 judge, direct sunlight does not penetrate to gi'eat depths. While 

 admitting that abyssal creatm-es are phosphorescent in their native 

 depths ; he regards as untenable the notion that any deep sea 

 animals see by the phosphorescent light emitted by thousands of 

 their neigbbours. 



The struggle for existence goes on as well in the dark silent 

 depths of the great ocean as in the busy whirl of civilized Ufe, and 

 in the shades and glens of primeval forests; and we can thence 

 conjectiu-e how these diverse organs, to which we have referred, are 

 mutually related. The lights which the blind fishes carry in their 

 two lanterns on their heads may serve at the same time to attract 

 their prey, and possibly give help to fishes who can see. Every 

 form having small eyes or small illuminating organs, being unable 

 to gain food, would be exterminated ; while none but the extremely 

 developed species would hold their own in the struggle. This 

 suggestion implies that the lantern-fishes of the deep sea being 

 bhnd, must have other means of distinguishing friend from foe, 

 and of identifying their prey. Such appears to be the case, for 

 from their proboscis or muzzle hang long feelers, beards, and the 

 like, at the tips or bulbous ends of which organs of sense or touch 

 may probably be situate. This matter has yet to be more fully 

 investigated ; and such inquiry is rendered more difficult by the 

 fact that, owing to the conditions of life at great depths, and pos- 

 sibly also to the mode of collecting specimens, the animals 

 brought up were all dead before reaching the surface. 



Though truly blind vertebrates are rare, eyeless invertebrates ' 

 are far more numerous. In some parts of the Continent of 



