554 



ZOOLOGY 



SECT. 



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 larvae of Stomatopoda are grotesque little creatures with a 

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



FIG. 439. Larva} of Crabs. A, Zotea-stage of Iftaja; B, Megalopa-stage of Portunua. 

 h. heart; it^ a 6 , abdominal segments; 1, antemmle ; ~\ antenna; I VIII, thoracic append 

 ages. (From Lang's Comparaticc Anatoma, after Glaus.) 



form, but in Isopoda the young leave the egg in the fori 

 curious maggot-like modification of the nauplius, which r 

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



form of a 

 remains 



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, 

 Pontellinn mediterranea, may almost be considered as aerial : it 

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

 manner of a Flying-fish. Some, like Lobsters, Crayfishes, &c., arc 



