476 DECAPODA. 



With reference to the development of the majority of the 

 Carabidae, Penaeinae, Palaemoninae, Crangoninae, it may be stated 

 generally that they leave the egg in the Zoaea stage (fig. 219) 

 with anterior appendages up to the third pair of maxillipeds. 

 The thorax is unsegmented and indeed almost unrepresented, 

 but the abdomen is long and divided into distinct segments. 

 Both thoracic and abdominal appendages are absent, and the 

 tail is formed by a simple plate with numerous bristles, not 

 forked, as in the case of the Zoaea of Fritz M tiller's Penaeus and 

 Sergestes. A dorsal spine is frequently found on the second 

 abdominal segment. From the Zoaea form the embryo passes 

 into a Mysis stage (fig. 220), during which the thoracic ap- 

 pendages gradually appear as biramous swimming feet; they 



FIG. 221. NEWLY-HATCHED LARVA OF THE AMERICAN LOBSTER. (After Smith.) 

 are all developed before any of the abdominal appendages, 

 except the last. In some cases the development is still further 

 abbreviated. Thus the larvae of Crangon and Palaemonetes 

 (Faxon, No. 476) possess at hatching the rudiments of the two 

 anterior pairs of thoracic feet, and Palaemon of three pairs'. 



Amongst the other Macrura the larva generally leaves the 

 egg as a Zoaea similar to that of the prawns. In the case of the 



1 Fritz Miiller has recently (Zoologisrher Anzeiger^ No. 52) described a still more 

 abbreviated development of a Pala-mon living in brooks near Blumenau. 



