CRUSTACEA OF THE DEEP SEA 127 



light of day. The clouds of luminous secretion thrown 

 out by Heterocarpus and other Prawns, and by certain 

 Mysidacea and Ostracods, may serve to baffle 

 pursuers, like the cloud of ink thrown out by a 

 Cuttlefish, and in some cases the more complex 

 organs may illuminate objects within the range of 

 vision. That this does not exhaust the possibilities 

 of speculation on the subject, however, is shown by 

 the case of certain deep-sea Prawns which have 

 been recently discovered to possess photophores 

 placed so as to illuminate the interior of the gill 

 cavities. What function they can discharge in this 

 position seems beyond conjecture. 



The colours of deep-sea Crustacea are very curious. 

 Few of them have the blanched appearance common, 

 for instance, in animals that live in the darkness of 

 caves ; on the contrary, their colours are often very 

 vivid, but they are nearly always uniform, without 

 spots or markings, and in a large proportion of cases 

 are in some shade of red or orange. This red colour 

 seems to be associated, in some way that we do not 

 understand, with the darkness of their habitat. The 

 general absence of markings is very striking. Dr. 

 Alcock remarks that in deep-sea Crustacea we never 

 see " those freaks of colour, or those labyrinthine 

 mottlings and dapplings, that excite our curiosity 

 when handling the Crabs and Shrimps of the reefs." 

 Possibly the explanation of this may be that in these 

 dwellers in darkness colour is merely, as it were, an 



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