CHARACTERISTIC PECULIARITIES 259 



The effects of living under a pressure that may 

 amount to anything between 300 lbs. and 3 tons 

 upon the square inch are not so astonishing as might 

 be expected. The tissues of Crustacea like Peiitacheles 

 (Fig. 60), which undoubtedly live on the bottom and 

 at the greatest depths, are certainly delicate, but not 

 more so than those of many oceanic species that live 

 near the surface, such as Sergestes. On the other 

 hand, there are few crustaceans that have a thicker 

 and harder "shell" (cuticular skeleton) than Glypho- 

 crangon (Fig. 52), Mtmidopsis (Fig. 58), and Gala- 

 cantha (Fig. 57), all of which assuredly are ground- 

 dwellers in abyssal depths ; and there are many other 

 forms, such as Dorodotes, Psalidopus (Fig. 21), and 

 Nephropsis (Fig. 59), in which the exoskeleton is at 

 least as hard as that of their relatives of the 

 shallows. 



Absence of sunlight affects Crustacea in the same 

 diverse ways — depending upon the original nature and 

 plasticity of the living material operated upon — that 

 it affects fishes, in some cases putting a premium upon 

 phosphorescence and owlish eyes, in other cases lead- 

 ing to degeneration or complete atrophy of the organs 

 of vision. 



Of the phosphorescent Crustacea of the deep sea, 

 the most brilliant observed in the Investigator are 

 Heterocarpus alphonsi (Fig. 15), from 480-750 fathoms, 

 and Aristcsus coruscans (Fig. 16), from 561-824 fathoms, 



