136 



THE CEAYflSH 



ii. The endopodite and exopodite are two many- 

 jointed filaments, the exopodite being sUghtly 

 the larger. 



D. The Gills and Gill-chamhers. 



The gills are highly vascular external outgrowths from 

 the] sides of the thorax and from its appendages. In them 

 respiration occurs, this process consisting in an interchange, 



Fia. 34. — Astacus fluviatilis. 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, (o. H. h.) 



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

 of gill. AM, arthrodial membraae. B, branoliiostegite. BG, branchio-cardiac 

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

 ES, endophragmal skeleton. H, heart, showing the dorsal ostia, with their 

 valves. L, liver. M, flexor muscle of the abdomen. K", nerve-connective. 

 P, proctodoeum. PB, podobranchia. PL, pleurobranchia. PS, pericardial 

 sinus. T, testis, with roots of vasa deferentia. V, sternal artery. VA, 

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

 muscles moving the limbs, which are not represented in the figure. W, one 

 of the legs, cut off! short. 



