370 



THE INVERTEBRATA 



the crayfish is lacking, and the bladder is prolonged into processes 

 which lie among the other viscera. 



In the nervous system (Fig. 276) the postoral ganglia are con- 

 centrated into a mass around the sternal artery. The vascular system 

 (Fig. 275) is on the same plan as that of the crayfish. The, gonads are in 



a.div. 



oph.a. 



hep. a. 



vasde 



(I aha. 

 Fig. 275. The shore crab, Carcinus maenas, dissected from the dorsal side 

 to show the viscera, a.div. left anterior diverticulum of the mid gut; an.a. 

 antennary artery; d.ah.a. dorsal abdominal artery (posterior aorta); h. heart; 

 hep. a. hepatic artery; Ir. liver; mdg. mid gut; oph.a. ophthalmic artery (an- 

 terior aorta); ost. ostium; p.div. posterior diverticulum of the mid gut; 

 St. "stomach" (proventriculus) ; t. testis; vas de. vas deferens. 



both sexes united across the middle line and prolonged laterally into 

 the carapace fold. Each oviduct bears a spermatheca. 



The first larva is a typical Zoaea (Fig. 277 A) with large compound 

 eyes, carapace, rostrum, short unsegmented thorax, and long strong 

 abdomen with forked telson. Of its thoracic limbs only the first two 



