BRACHYURA. 



295 



transition from the swimming to the creeping manner of life, and in 

 the most important points of its segmentation ah'eady agrees with 

 the adnlt. In the condition of the abdomen, the Megalopa is some- 

 what on a level with an adult Anomuran Decapod. The anterior 

 part of the body with the limbs already shows the typical Brachyuran 

 character. The youngest Megalopa stages, however, still in most 

 cases carry on the dorsal shield traces of the former Zoaean spines 

 (Fig. 139 A). The limbs have now attained their final shape; 

 the maxillipedes have lost the locomotory function and are com- 





Fio. 139. — Three ontogenetic sta^'es of Con-inn^ maencts. A, younger, and B, older Megalopa 

 stage. C',|young crab. {A, after Spence Rate ; D and C, after Bkook). </, dorsal .spine ; 

 1', rostrum. 



paratively smaller. The ambulatory limbs, on the contrary, have 

 developed greatly. The abdonaen is still stretched out backwards, 

 and shows theifpleopoda as swimmerets provided with long setae ; 

 these consist of^a basal joint and an oval terminal plate provided 

 with setae (exopodite), while the quite short endopodites furnished 

 with small hooks,-[as retinacula, serve to connect the right and left 

 swimmeret, and consequently bring about a simultaneous movement 

 of the two limbs. The forked telson of the Zoaea has changed 

 into a rounded caudal plate. 



