GENERAL BIOLOGY 68i 



migrate all over the abyssal plain of the oceans, have very large 

 eyes, the diameter of the eyes in Macrin^us armatus, for 

 instance (see p. 417, and Fig. 272, p. 398), being equal to one- 

 fifth of the length of its large head. 



As regards pelagic fishes we must remember that light 

 penetrates to far greater depths than was previously supposed, 

 for, as already stated, in the Sargasso Sea photographic plates 

 were strongly acted upon by light at 500 metres, and at 1000 

 metres traces of light were clearly perceptible, so that at least 

 certain components of the sunlight penetrate to that depth. 



If we now review the size of the eyes of the fishes in 

 relation to their vertical distribution, we notice a strange 

 change just about the bathypelagic limit often referred to in 

 this book, viz. 500 to 750 metres, varying according to latitude. 



Fig. 497. 

 Cetotnimiis storeri, G. and B. Nat. size, 12 cm. 



In the fish taken between 150 and 500 metres the diameter of 

 the eye compared to the length of the head is, according to 

 Brauer, as follows : — 



Stomias about 1:4 Argyropelecus about i : 2 



Chauliodus „ 1:4 Sternoptyx „ 1:2 



Ichthyococcus „ 1:2.6 Opisthoprocttis „ 1:4 

 VincigKerria ,, 1:3 



If we consider Cyclothone and other fish which live deeper 

 than 500 metres we find the following relations : — 



Cyclothone signata 1:12 (see Plate 1.) 

 ,, microdon 1:12 (see Plate I.) 



,, obsaira i : 15 or 20, 



and if we inspect the figures representing Gastrostomus bairdii 

 (Fig. Z'x^ ^' P- 97)' Cyema atrufn (Fig. 69, p. 87), and Gonostoma 

 (Plate II.), we obtain a still stronger impression of the small 

 size of the eyes. Finally our deepest pelagic hauls contained 

 blind forms which have never been taken in the upper layers ; I 

 reproduce two of these blind fishes (Figs. 497 and 498), of 



