PIGMENT INDEPENDENT OF LIGHT. 87 



must of course have been carried on among the various crear 

 tures on the floor of the ocean, every form having small eyes 

 or small illuminating organs, being unable to see clearly or 

 to give enough light, must soon have been exterminated, while 

 none but the most extremely developed species could hold their 

 own in the struggle. Newly introduced varieties must there- 

 fore have been able to develope either larger eyes and keener 

 vision, or else strongly illuminating organs, in order to escape 

 annihilation. This evidently presupposes that the lantern 

 fishes of the ocean-depths, being blind, must have other mean.? 

 for distinguishing and identifying the prey or the foes that 

 approach them ; and this seems in fact to be the case, for from 

 their proboscis or muzzle depend long feelers, beards, and the 

 like, and at their tips or bulbous ends, organs of touch or of 

 smell might easily be situated which could serve such a 

 purpose. 



Special instances of the influence of light on animals. 

 There are numerous special influences exercised by the different 

 degrees of intensity of light or by its periodical changes on the 

 different functions of the animal organism ; but those only 

 interest us which may now be regarded as directly connected with 

 the fitness for life of a species under certain external conditions 

 of existence. Thus we may entirely leave out of consideration 

 the influence, for example, of red light on the formation of 

 carbonic acid during respiration, the difference of the amount of 

 carbonic acid exhaled by day and by night, and others ; although 

 these processes are of the utmost importance for the life both of 

 the organs and of the animals. If we thus dispose of these and 

 other similar effects of light, there remain two points which we 

 must discuss ; the first being the presence or absence of pigment 

 in the skin of the animal and the chromatic function, as it is 

 termed. 



All animal pigments in the skin were formerly regarded as 

 arising from the direct influence, of light upon the skin, and, as 

 a necessary corollary to this view, it was also a;sserted that the 

 absence of Kght always prevented the formation of such pig- 

 ments, or destroyed that which was already formed. The fact 

 that the greater number of cavern animals and almost aU 



