600 



ZOOLOGY 



soma: it has broad, depressed cephalic and thoracic shields of 

 glassy transparency : the abdomen is very small and the legs 

 extremely long and biramous. Lastly, in the Fresh-water Cray- 

 fish the young resemble the adult in all but proportions and 

 certain unimportant details of structure. Thus in the series of 

 Decapoda we get a gradual abbreviation in development, stages 

 which are free larval forms in the lower types being hurried 

 through before hatching in the higher. 



The larvas of Stomatopoda are grotesque little creatures with a 

 very large spiny carapace. In Amphipoda there is no free larval 



Fig. 475.— Larva) of Crabs. A, Zowa-stago of Maja ; B, Megalopa-stago of Portunus. 

 It, heart ; a% — a 6 , aVjdominal segments ; 1, antennule ; t t antenna ; J — VI11, thoracic append- 

 ages. (From Lang's Comparative Anatomy, after Claus.) 



form, but in Isopoda the young leave the egg in the form of a 

 curious maggot-like modification of the nauplius, which remains 

 in the brood-pouch until it has attained the adult form. 



Ethology.— The Crustacea are remarkable for their very perfect 

 adaptation to the most various conditions of life : they occur in 

 fresh-water, in the sea, in brine-pools, in subterranean caves, and 

 on land : of the marine forms some are littoral, some pelagic, some 

 abyssal, descending to over 3,000 fathoms. One species of Copepod, 

 Puntcllina mediterranea , may almost be considered as aerial : it 

 is described as taking long flying leaps out of the water, after the 

 manner ef a Flying-fish. Some, like Lobsters, Crayfishes, &c, are 



