•2-2 



artery in the fourtli abdominal segment. In the last 

 sesrment an artery is o-iven oit' internally to the intestine, 

 on the ventral side of which it anastomoses Avith its fellow 

 and the sub-intestinal artery. The abdominal artery 

 finally terminates in the uropoda. 



The venous system is lacunar. A large thoracic 

 sinus runs into the abdominal sternal sinus, from which 

 five afferent branchial vessels arise; each of these 

 bifurcates at the base of the branchial appendages, 

 supplying the superior and inferior lobes of the branchiae. 



The vascular system of the branchiae. The branchiae 

 are supplied by venous vessels from the abdominal sinus. 

 The efferent branchial vessels open into the pericardium 

 by way of the branchio-pericardial canals (PI. II., fig. 16, 

 hr.p.c). The circulation in the superior and inferior lobes 

 of the abdominal appendages, both of which are respira- 

 tory, is different. The interior of the inferior lobe of 

 the branchiae [inf. lam.) is fenestrated by an irregular 

 system of lacunae, those of the outer side containing 

 venous blood and those of the inner side arterial. On the 

 other hand, the vascular system of the superior lobe [stip. 

 lam.) is very definite and uniform throughout the five 

 pairs. It consists of a venous portion (PL II., fig. 13, a.h.v.), 

 which is ventral (looking at the gill from the anterior face) 

 to the arterial system of vessels (e.h.v.). The individual 

 arteries and veins interdigitate in a very complete manner, 

 and the vascular supply is veiy rich, as will be seen by 

 reference to the figure (PL III., fig. 3). On this account, 

 the superior gills cannot be looked upon as beng merely 

 opercular in function in this animal, but are certainly 

 respiratory appendages of a very perfect nature. 



The blood is colourless and contains nucleated 

 corpuscles which vary in size. As in most anthropods, it 

 is Yery coagulable. 



