ANNULOSA I CRUSTACEA. 



247 



to be none in the Cray-fish (Astacus fluviatilis). Fritz Miiller, 

 again, has shown that the primitive form of one of the Shrimps 

 (Peneus) is that of a " nauplius." This section comprises the 



Fig. 95. Macrura. Common Lobster (Homarus -vulgaris). 

 constituting the great chelse or ninnin^-rlaws : 2. Second D; 

 3. Third pair of le,"" o1 " " ; 

 simply pointed exti 



crura. Common Lobster (ffomarus vulgaris). i. First pair of legs, 

 the great chelse or nipping-claws ; 2. Second pair of legs, also chelate ; 

 ir of legs, also chelate ; 4 and 5. Last two pairs of ambulatory legs, with, 

 ted extremities ; a Antennules ; go. Great antennae ; ca Carapace. 



Lobster, Cray-fish, Shrimp, Prawn, &c., of which the Lobster 

 may be taken as the type. 



The form proper to the adult is not attained until after several moults, 

 constituting a genuine metamorphosis, though one which is effected by very 

 gradual stages. 



