144 



THE CEAYFISH. 



branohiostegite. 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 

 chamber is occupied by the gills ; but in front of 

 them, and just behind the line of the cervical groove, 

 is a channel, the cervical canal.. In this canal the 

 scaphognathite works to and fro with a scuUing 



Fig. 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, (c. h. h.) 



AB, artlivobraiicliia : only one is figured on eacli side. AF, afferent 

 vessel of gill. AM, ortlirodial membrane. B, branchiostegite. BO, 

 branohio-cardiao canal. EI", efferent vessel of pill. EM, extensor muscle 

 of tlie abilcinien. ES, endopliragmal skeleton. H, heart, shoiving the dorsal 



ventral thoracic artery. VA, artery supplying leg. VS, ventral blood- 

 sinus: it contains numerous large muscles moving the limbs, which aie not 

 represented in the figure. "W, one of the legs, out off short. 



