Crustaceans. 



47 



below the carapace, a feature to which the popular English 

 name is due. Like the httle shrimp [Hipfolyie) previously 

 mentioned, the opossum shrimp can make itself almost invisible 

 by assimilating to the colour of its surroundings, passing from 

 light grey to dark brown, or even black, wthin the space of 

 less than half an hour. As in the decapods, the eyes of Mysis 

 and its allies are stalked, the niajoritj' of the lower crustaceans 

 having these organs sessile and almost flush with the surface of 

 the head. 



EverA'one who has walked or sat on a sandy beach at low 

 tide is familiar with the little Sand-hoppers {Talitnis saliafor) 



FIG. 51. SAND-HOPPER (AFTER SARS). 



which appear in thousands, leaping and skipping about with 

 extraordinary agihty (Fig. 51). The Sand-hopper belongs to a 

 division of sessile-eyed Crustaceans known as Amphipods, in 

 which a conspicuous carapace is absent, nearh? the whole of the 

 much-compressed body being ringed or segmented. The pecuHar 

 jumping movements are produced by the sudden straightening 

 out of the muscular abdomen, the last three segments of which 

 are provided with special rod-hke appendages modified for the 

 purpose ; the remainder of the appendages of the body consist 

 of pincers, walking-legs and swimmerets. The Sand-hoppers have 



