134 



THE CRAYFISH 



1. The branchial chambers are situated one at each side of 

 the thorax, between the body and- the branchiostegite. 



Expose the left branchial chamber by cutting away the 

 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 epimera, and on its outer side by the 



Fig. 26. — 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, (c. H. H.) 



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

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

 canal. EP, efferent vessel of gill. SM, extensor muscle of the abdomen. 

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

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

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

 sinus. T, testis, with roots of vasa def erentia. 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, out off short. 



