170 ZOOLOGY. 
has been separated from the others. For the finer structure 
of the body-walls see Fig. 116. 
The alimentary canal consists of a mouth, a pharynx 
armed with two large teeth and much smaller ones. The 
pharynx is entirely everted during the act of taking its food. 
Into the esophagus empty two large salivary glands; the 
remainder of the alimentary canal is straight and tubular. 
The circulatory system is very complicated ; it is closed and 
the blood is red. Both the dorsal and ventral vessels are 
contractile, the blood flowing forward in the dorsal vessel. 
and backward in the ventral vessel. The two small vessels, 
one on each side, in each segment of the body, branch off 
from the ventral vessel and subdivide, each sending a branch 
to the ventral ramus of the foot of the segment behind, and 
another larger branch around the intestine to the dorsal ves- 
sel, receiving also, on its way, a vessel from the upper ramus 
of the foot of its own segment. ‘‘ Besides these principal 
lateral vessels, there are five other vessels on each side 
in each segment, coming from the ventral vessel. These 
form a loose but regular net-work that surrounds the in- 
testine and is connected with five other convoluted vessels, 
which join the dorsal vessel. This net-work on the intestine 
probably supplies the hepatic organ with material for its 
secretion, and very likely may receive nutritive material from 
the digested food.” (Turnbull, Trans. Conn. Acad., iii. 1876.) 
The blood is aérated in the finer vessels of the oar-like feet 
and in those situated about the alimentary canal. The 
nervous system consists of the “brain” and ventral double 
ganglionated cord. 
The sexes of Nereis virens are separate; the eggs during 
the breeding season fill the body-cavity, and pass out through 
certain of the segmental organs, which act as oviducts, while 
others, probably the more anterior ones, are excretory, like 
the kidneys of vertebrates, as urea has been detected in them. 
These organs are situated at the base of the lower ramus of 
each foot. In some species of the Capitellid@ Hisig has found 
that it is normal for several segmental organs to be present 
in a single segment. 
While the mode of development of our Nereis has not 
