364 THE CRAYFISH chap. 



heart. Thus in virtue of the successive contractions of the 

 heart and of the disposition of the valves, the blood is kept 

 constantly moving in one diVection — from the heart by 

 the arteries to the various organs of the body, where it 

 receives carbon dioxide and other waste matters ; thence by 

 sinuses into the great sternal sinus ; from the sternal sinus 

 by afferent branchial veins to the gills, where it exchanges 



af.br V 



uii5; St s 



Fig. 89. — Bingram illustrating the course of the circulation of_ the blood in the 

 Craj'fish. Heart and arteries red ; veins and sinuses containing non-aerated 

 blood blue ; veins and sinuses containing aerated blood pink. The arrows show 

 the direction of the flow. 

 The blood from the pericardia! sinus (pcd. s) enters the heart iht) by a valvular 

 aperture {v^.) and is propelled into arteries {a\ the orifices of which are guarded 

 by valves (z/-.) ; the ultimate branches of the arteries discharge the blood into 

 .sinuses (j), and the sinuses in various parts of the body debouch into the sternal 

 sinus i^st. s) ; thence the blood is taken by the aflferent branchial veins 

 {a/, br. 7') into the gills, where it is purified and is returned by efl^ertnt branchial 

 veins {e/. br. 7/) into the branchiocardiac veins ii>r. c, 7') which open into the 

 pericardial sinus. (From Parker and Haswell's Zoology.') 



carbon dioxide for oxygen ; from the gills by efferent branchial 

 veins to the branchiocardiac veins, thence into the peri- 

 cardial sinus, and so to the heart once more. 



It will be seen that the circulatory system of the crayfish, 

 like that of the frog, consists of three sections — (i) the heart, 

 or organ of propulsion ; (2) a system of out-going channels, 

 the arteries, which carry the blood from the heart to the 



