86 The Under-Water World 



walk poised upon stilts. Other notable 

 features of these Crustacea are the enor- 

 mous size of their eyes and their 

 luminosity. One deep-sea prawn at 

 least can pour out from glands at the 

 base of its antennae rolling clouds of a 

 ghostly pale blue light that can illumi- 

 nate surrounding objects. Others are lit 

 up by special organs " photophores " 

 upon their bodies or heads. The light 

 may serve a variety of purposes. It may 

 attract prey, light up hunting grounds, 

 or help to keep the shoal together. 



The short-tailed Crustacea or crabs are 

 derived from lobster-like animals that by 

 a constant " tucking-in " of the tail, the 

 better to burrow or hide in rock fissures, 

 have reduced that organ until it serves 

 merely to support the ova. No crab can 

 use its tail to project itself forcibly 

 through the water in the manner of a 

 shrimp or lobster. The diversity of form 

 amongst crabs is remarkable. Some 



