LACK-LUSTRE EYES 263 



other explanation for the degeneration of its eyes. 

 The explanation is, I think, found in the fact that it 

 lives only in very muddy water, that is to say, in 

 1 darkness after all. 



Eyes of fair size, but deficient in colour and with- 

 out facets, are very frequently met with among the 

 sedentary Crustacea of the profundities of the ocean. 

 Of the 241 species of Malacoslraca dredged by the 

 Investigator in the depths, more than 20 per cent, 

 show this characteristic form of degeneration. For 

 instance, in Plastocrangon cceca, from 561 fathoms (Fig. 



56) , the eyes are quite distinguishable, but instead of 

 being faceted they have a smooth, dead surface, and 

 their colour is a pale chalky yellow. The same 

 pallid, milky-yellow, lack-lustre eyes, which, though 

 they may perhaps serve to distinguish between light 

 and darkness, can never form a definite visual image, 

 characterise the species of Galacantha (Fig. 57) and 

 the innumerable species of Munidopsis (Fig. 58), 

 which are found nowhere but in the sullen bottoms 

 of the deep. Unhappily, eyes of this sort cannot be 

 properly portrayed in uncoloured figures. With respect 

 to these figures, it should be observed that Munidopsis 

 (Fig. 58) is drawn in the natural position with the 

 after half of the tail folded, v/hile Galacantha (Fig. 



57) has been placed in a conventional attitude which 

 it does not adopt in life. 



In Nephi^opsis (Fig. 59), which in all probability 



