ETTPAGTTRtrS. 519 



up to a point, in that it gives segmental branches to the 

 remaining thoracic limbs, but in the adult, and in all 

 probability in the larva, it never passes into the 

 abdomen. This artery, in fact, divides in the sixth 

 thoracic somite into right and left branches, which 

 supply the last pair of pereiopods. Small ascending 

 arteries are given off with all the branches to the 

 pereiopods. 



The blood supply to* the abdomen is entirely carried 

 by the Superior Abdominal artery (5. abd.), and the 

 vessel has undergone remarkable adaptation for its extra 

 duties. A large trunk leaves the heart just above the 

 sternal artery and passes above the gut — only giving off 

 small branches — as far as the first abdominal segment. 

 Here it divides into two large vessels. One {seg. a.) 

 passes directly downwards to the right, turns backwards, 

 and runs on the top of the flexor muscles. It divides 

 in the third segment into sub-muscular and supra- 

 muscular branches. The former follows the course of 

 the nerve cord and terminates near the last ganglion; 

 the latter gives numerous branches to the liver and 

 gonads and finally divides into branches supplying the 

 uropods, telson and rectum. The other vessel (s. abd.), 

 veering slightly to the left, continues on the surface of 

 the liver and supplies the gonads and pleopods. In the 

 female we have the interesting condition that each ovary 

 is partly supplied by one vessel and partly by the other 

 (fig. 27); in the male the morphological left testis is 

 supplied by the ventral (right) branch, while the right 

 testis is supplied by the dorsal (left) branch. 



M. T. Thompson finds in the young animal that the 

 fourth zoea and the glaucothoe stages have a superior 

 abdominal vessel with segmental branches, but that on 

 the metamorphosis into the adult all these branches aire 



