CHAPTER XVIII 



THE DEEP-SEA CRUSTACEA OF THE INDIAN OCEAN 



(continued) 



As might be expected, arrangements which appear to 

 be meant to counteract obscurity of light and defects 

 of vision are to be found among the Crustacea of the 

 deep sea. Quite a number of blind and purblind 

 species, or of species living in darkness, can be named 

 whose sense of smell, as evidenced by a remarkable 

 thickening of the outer or olfactory lash of the first 

 pair of antennae, must be much above the average. 

 This enlargement of the olfactory organ is seen in 

 Nephropsis carpe7tteri (Fig. 59) : it is even better 

 marked in Pentacheles hextii (Fig. 60), and Plasto- 

 crangon cceca (Fig. 56), and best of all in Glypho- 

 crangon priononota (Fig. 52). In Pentacheles, too, the 

 basal joint of the same pair of antennae, in which 

 joint the organ of hearing is lodged, is very sugges- 

 tively increased in size, as it also is in the blind 

 Prionocrangon ommatosteres (Fig. 20). 



The influence of darkness on the colouring of the 

 deep-sea Crustacea is as well marked as it is on that 



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