276 F. M. Turnbull — .hiatomy and Mabits of Nereis vireus. 



(?;) passes to the base of the head, where it joins tlie dorsal vessel 

 («), thus completing the circulation. From tliis junction small 

 vessels probably go into the head and antennae. The lateral vessel 

 passing to the lower ramus divides into branches ramifying on that 

 portion which is continuous with the foot on the ventral side of the 

 segment, and also over the lower ramus (tigs. 22 and 26). There a 

 connection is made with vessels of the upper ramus, and I think 

 this is done by the vessel marked x in figures 22 and 24, because it is 

 quite large at the base of the inferior ligula of the upper ramus, and 

 grows smaller at first and then swells out again before joining the 

 vessels of the iipper ramus, in the superior ligula. The branch d 

 (figs. 20, 22 and 24), coming from the dorsal ramus, receives blood 

 from that organ and also from a peculiar and beautiful arrangement 

 of capillaries on the dorsal side of the body (fig. 25). 



In the first four segments, in the region of the proboscis, the dorsal 

 vessel has no branches, but in the remaining segments, commencing 

 with the fifth, it has five pairs of long peripheral branches (fig, 20, e, c'), 

 corresponding to the peripheral vessels of the posterior part of the 

 body. They are not attached to the proboscis, but are simply con- 

 nected with the dorsal and ventral vessels by their ends. The one 

 coming from the dorsal vessel in the fifth segment is connected with 

 the ventral vessel in the fourth segment (fig. 20.) The first three 

 feet probably do not act as gills, as very little blood is sent to them. 

 The two networks (figs. 20 and 21, u) on the proboscis are probably 

 for carrying on the exchange between the blood and the liquid of the 

 body cavity. 



The respiration is carried on by the red fluid in the beautiful ar- 

 rangement of capillaries on the body and feet, especially the latter. 

 The flat ligulie of the feet are exceedingly delicate in structure and 

 take the place of gills, absorbing the oxygen from the water to purify 

 the blood received from the ventral vessel, which then returns to the 

 dorsal vessel. 



The disposition of this respiratory arrangement is shown in figures 

 22, 24, 25 and 26. 



Tlie Nervous System. 



^ If Tuw - 



The nervous system of Nereis vi7^ens {Ggs. 27 and 28) is complicated 



and well developed, being composed of a series of ganglia, sending 



out branches and connected by nervous cords. It lies mainly on the 



ventral floor of the body beneath the large ventral vessel. The first 



and largest ganglion (figs, 27 and 28, a), analogous to the brain of 



higher animals, is situated in the head. It is composed of several 



