254 CIRCULATION IN CRUSTACEA. 



ratus of a Lobster is seen in fig. 141, in which, a is the heart ; 

 6 and c, the arteries to the eyes and antennae ; d, the hepatic 

 artery ; and e and f, the arteries which supply the abdomen 

 and thorax. The blood that has been propelled through these 

 by the action of the heart, finds its way into the great venous 

 sinus g g } which receives the fluid collected from all parts of 

 the body ; from this it passes to the gills, h ; and thence it 

 is returned to the heart by the branchial veins, i. Another 

 view of a portion of the circulating apparatus is given in fig. 

 14:2, which represents a transverse section of it in the region 



b ve c f vb 



st ce 

 Fig. 142. BRANCHIAL CIRCULATION OF LOBSTER. 



of the heart, with one pair of gills. The heart is seen at c ; 

 and from its under side proceeds one of the arterial trunks 

 which convey the blood to the system. Returning thence, 

 the blood enters the venous sinus s, which has an enlarge- 

 ment at the base of each gill ; and this seems to act the part 

 of a branchial heart, like the corresponding enlargement on 

 the branchial vessels of the Cuttle-fish. From this cavity, it 

 is carried by the vessel va into the branchiae 5 ; and after it 

 has passed through the capillaries of the gill-filaments, it is 

 collected by the vessels ye, which carry it to the branchial 

 veins, v!>, and thence to the heart. The general plan of the 

 circulation in this class is shown in fig. 132. 



293. In the class of INSECTS we find a still greater incom- 

 pleteness in the system of vessels for the conveyance of blood. 

 Arterial trunks can only be traced to a short distance from 

 the dorsal vessel, which answers the purpose of a heart ; and 

 the nutritive fluid which they convey is delivered into the 

 channels or sinuses that exist among the different organs. 



