394 



DEC A POD A. 



FIG. '219. LARVA OF HIPPOLYTE 

 IN ZCKEA STAGE. (From Claus.) 



MX', and MX", maxillae 1 and 2; 

 Mf. Mf". Mf". maxillipeds. 



generally that they leave the egg in 

 the Zoa-a stage (fig. 219) with an- 

 terior appendages up to the third 

 pair of maxillipeds. The thorax is 

 unsegmented and indeed almost un- 

 represented, but the abdomen is long 

 and divided into distinct segments. 

 Both thoracic and abdominal appen- 

 dages are absent, and the tail is 

 formed by a simple plate with nu- 

 merous bristles, not forked, as in the 

 case of the Zooea of Fritz Muller's 

 Penasus and Sergestes. A dorsal 

 spine is frequently found on the 

 second abdominal segment. From 

 the Zoam form the embryo passes 

 into a Mysis stage (fig. 220), during 

 which the thoracic appendages gra- 

 dually appear as biramous swim- 

 ming feet ; they are all developed 

 before any of the abdominal ap- 

 pendages, except the last. In some 

 cases the development is still further 

 abbreviated. Thus the larvse of 

 Crangon and PalaBmonetes (Faxon, 

 No. 476) possess at hatching the 

 rudiments of the two anterior pairs 

 of thoracic feet, and Palsemon of 

 three pairs 1 . 



FIG. 220. OLDER LARVA OF HIPPOLYTE AFTER THE THORACIC APPENDAGES HAVE BECOME 



FORMED. (From Claus.) 



1 Fritz Miiller has recently (Zoologischer Anzeiger, No. 52) described a st'.ll more 

 abbreviated development of a Pabcnion living in brooks near Blumenau. 



