OF THE BLOOD AND CIECULATION. 



205 



place of veins ; these venous sinuses swell out at the base, and 

 send a branch to each bran- 

 chia. After having circulated 

 through these organs, the 

 blood is returned to the 

 heart, to perform a similar cir- 

 cuit. 



[ 370. In insects (fig. 

 the circulation is main- 

 tained by a dorsal vessel (a), 

 which acts the part of a 

 heart : it is divided into seve- 

 ral chambers by valves, which 

 permit the blood to flow only 

 towards the head ; the vessel 

 here appears to cease, and the 

 blood seems to flow in the 

 interspaces of the tissues ; cur- 

 rents of globules form arches 

 in the antennae, wings, legs, 

 and the prolongations of the 

 abdomen ; lateral currents 

 are seen at b, the direction of 

 their course being indicated 

 by the arrows. The circulation 

 Fig. 222. 



Fig. 221. Circulating organs of the 

 Doris. 



in insects can only be 



ular system of the lobster. 



.d in transparent aquatic larva, as those of the 



i, in which it forms a beautiful spectacle for the 



microscopist. The chyle globules enter the dorsal vessel by 



