CIRCULATORY SYSTEM. 157 



b. The heart is a polygonal thick-walled muscular 



sac lying in the pericardial sinus. If living it will 

 be seen to contract rhythmically. It receives 

 blood from the pericardial sinus by three pairs of 

 valvular apertures, the ostia, of which the dorsal 

 pair will be easily seen. The lateral and ventral 

 pairs will be better seen at a later stage of the 

 dissection. 



c. The roots of the arteries are rather small and trans- 



parent, and hence difficult to see. They arise 



from the two ends of the heart, and should be 



noticed at the present stage of the dissection, 



though the arteries themselves are best seen in 



an injected specimen, and will be described later 



(p. 167). 



i. From the anterior end of the heart arise a median 



ophthalmic artery and a pair of antennary 



arteries ; and behind and below these a pair of 



hepatic arteries. 



Fig. 37. Astacus pallipes, var. nobilis. Dissection of a male from 

 the right side. The right sictaof the body-wall with its appendages 

 and the right side of the oesophagus, stomach, and mesenteron 

 have been removed. The thick black line represents the cut edge 

 of the cuticle, (c. H. h.) 



A, endophragmal skeleton. AA, antennary artery. AU. 'auditory' sac. 

 B, basipodite of the tenth appendage. BD, aperture of left bile-duct into the 

 mesenteron C, cardiac chamber of the stomach. CM, caecum. CO, cardiac 

 ossicle. CP, middle joint of tenth appendage. CP9, middle joint of ninth 

 appendage. CX, coxopodite of tenth appendage. D, terminal joint of 

 same. DA, dorsal abdominal artery. E, eye. G 1, supra-oesophageal gan- 

 glion. G 2, sub-oasophageal ganglion. G 3, second post-cesophageal ganglion. 

 G 8, last thoracic ganglion. G 14, last abdominal ganglion giving off posterior 

 visceral and other nerves. H, right lateral ostium of the heart. H A, hepatic 

 artery. |, proctodceum. IS, first joint of tenth appendage. K, kidney. 

 L, fiver. LT, lateral tooth. M, second joint of tenth appendage. MS, 

 metastoma. MT, median tooth, m 8, second joint of eighth appendage. 

 Nl, N 3, etc., endopodites of first, third, etc., appendages. OA, ophthalmic 

 artery. OC, left para-cesophageal connective : the greater part of the right 

 one has been removed. OE, oesophagus. PL 16, pleuron of the sixteenth 

 segment. PO, pyloric ossicle. PPO, prepyloric ossicle. PR, propodite of 

 the tenth appendage. PTO, pterocardiac ossicle. PY, pyloric chamber of 

 the stomach, p 3, p 4, etc., protopodites of the third, fourth, etc., appendages. 

 R, rostrum. SA, sternal artery, s 16, sternum of the sixteenth segment. 

 T, testis : the right anterior lobe has been removed. T 16, tergum of the 

 sixteenth segment. U, ureter. UA, aperture of the ureter. UCO, urocardiac 

 ossicle. V, ventral thoracic artery. VA, ventral abdominal artery. VD, left 

 vas deferens : the right one has been cut off short. VDA, aperture of the left 

 vas deferens. X 1, X 2, etc., exopodites of first, second, etc., appendages. 

 ZO, zygocardiac ossicle. 1 4, the fourteenth appendage. 



