444 



DISTRIBUTION IN SPACE AND TIME 



which such plasticity was absent. It is also clear that species 

 which spend more or less of their time in the uppermost part of 



the abyss (and even in the Pelagic zone) 

 have a better chance of improving their 

 organs of vision. But the matter is still 

 in the conjectural stage. 



Some of the fishes which see indif- 

 ferently or not at all partly make up for 

 the deficiency by the possession of long 

 feelers, derived from fin - rays, which 

 serve as a means of exploring the sur- 

 rounding area to some distance (see 



P . 2 8). 



Deep - Sea Molluscs (Mollusca].- 

 Some of the deep-sea Cuttle- Fishes (e.g. 

 Taon^^ts abyssicola, fig. 1297) are dis- 

 tinguished by the possession of excep- 

 tionally large eyes. The species figured 

 has been dredged from depths of 902- 

 1370 fathoms in the Indian Ocean. 

 There are also several curious Octopods 

 (see vol. iii, p. 33). The Snails and 

 Bivalves possess unusually thin and fragile shells, while some of 

 the former have lost the characteristic rasping -organ (odontophore). 



Fig. i297.-Deep-s C a Cuttie- 



abyssicola] with large eyes 



Fig. 1298. Deep-Sea Prawn (Glyphocrangon priononota) with large eyes, and well-developed organs of smell 



Deep -Sea Crustaceans (Crustacea]. Pink and red are here 

 the prevailing colours, but some forms are purple, yellow, cream- 



