152 



THE CRAYFISH. 



branchiostegite of that side; and fix the animal on its right 



side under water. 



The chamber is bounded on its inner side by 

 the thoracic wall, and on its outer side by the 

 branchiostegite. It is open below and behind, and 

 the former opening is partially stopped by the basal 

 segments of the legs. The greater portion of the 



Fig. 3G. Astacus pallipes. Diagrammatic transverse section through 

 the thorax. The dotted spaces contain arterial blood. The spaces 

 shaded with horizontal lines contain venous blood. The arrows 

 indicate the direction of the blood circulation, (c. H. h.) 



AB, arthrobranchia : only one is figured on each side. AF, afferent vessel 

 of gill. AM, arthrodial membrane. B, branchiostegite. BC, branchio-cardiac 

 canal. EF, efferent vessel of gill. EM, extensor muscle of the abdomen. ES t 

 endophragmal skeleton. FM, flexor muscle of the abdomen. H heart, showing 

 the dorsal ostia, with their valves. L, liver. N , nerve-connective. P, procto- 

 deum. PB, podobranchia. PL, pleuro-branchia. PS, pericardial sinus. T, 

 testis, with roots of vasa deferentia. v, ventral thoracic artery. VA, artery 

 supplying leg. VS, ventral blood-sinus : it contains numerous large muscles 

 moving the limb3, which are not represented in the figure. W, one of the 

 legs, oat off short. 



