INTRODUCTOEY. 37 



The real obstacle to the theory — to my mind a fatal objection 

 — is the fact that in many cases the eyes are evidently in coarse 

 of degeneration. This is not apparent on a mere inspection of 

 the eyes ; they require to be studied microscopically. It often 

 happens that the external part of the eye — the facetted 

 " cornea " — is the last part to vanish, and that even the 

 pigment may persist long after the visual elements have 

 become so degenerate as to be unrecognisable. 



There are so many cases among the deep-sea animals of 

 degenerate eyes, that it seems reasonable to suppose that vision 

 is impossible ; the presence of well-developed eyes or the total 

 absence of these structures are, as has been explained, intelligible 

 on the theory of abyssal light ; not so the existence of eyes in 

 an intermediate condition. The inevitable conclusion, there- 

 fore, from these facts appears to be that the brilliant and varied 

 colorations of deep-sea animals, is totally devoid of meaning ; 

 they cannot be of advantage for protective purposes or as warn- 

 ing colours, for the single and sufficient reason that they are 

 invisible. 



It might possibly be argued that the colours in question had 

 at one time a secondary use, and had in fact been produced for 

 such purposes,- — at the time when the animals were restricted 

 to shallow waters, accessible to the sunlight. These have been 

 preserved, it would then be suggested, owing to the fact that 

 sufficent time had not elapsed since migration into deep water, 

 for their disappearance or modification. 



lu the case of some organisms this suggestion may be 

 allowed, as it is really not worth combating ; but it is generally 

 admitted that a great part of the deep-sea fauna dates from 

 extreme antiquity. Professor Moseley fixes the Cretaceous 

 epoch as the commencement of the colonisation of the abysses ; 

 this period is quite remote enough, though others would put it 



