Crustaceans 79 



limbs being discarded and renewed after 

 the next moult. Propagation in these 

 animals is always effected by means of 

 eggs which usually hatch into larvae quite 

 unlike the parent form. 



A number of the animals included 

 in this group are familiar owing to their 

 large size and economic value. The 

 Crustacea differ from the insects and 

 arachnids in having two pairs of antennae 

 in front of the mouth ; in the possession 

 of three or more pairs of jaws behind 

 the mouth, in the peculiar disposition 

 of the " walking legs/' and, with very 

 few exceptions, in breathing by means 

 of gills. The Macrura, or long-tailed 

 crustaceans, includes the prawns, shrimps, 

 lobsters and crayfishes. These, together 

 with the hermit crabs and true crabs, 

 are known as the Decapod or ten-footed 

 crustaceans, having five pairs of legs, 

 the first being often developed to form 

 pincers which may, as in certain lobsters 



