ANATOMY AND HISTOLOGY OF PLEUROCH ATA MOSELEYI. A495 
glands are columnar, each provided with a nucleus, the outer border of the 
cell is hyaline, and does not stain deeply with colouring reagents. 
The existence of these highly specialised glands is no doubt the most 
remarkable point in the anatomy of Pleurochwta, and their presence may 
perhaps be correlated with the absence of segmental organs, 
Circulatory System. 
The fact that the specimens at my disposal were preserved in spirit, hindered 
very accurate researches into the distribution of the smaller branches of the 
vascular system; but in the case of the more important vessels, their large 
size, and the frequent presence of coagulated blood, rendered their study fairly 
easy. Consequently, the following description is, I hope, correct for the main 
trunks of the vascular system, but some errors may have crept in with respect 
to the smaller vessels. 
The vascular system of Pleurocheta consists of six longitudinal trunks. 
(1) The dorsal vessel, (2, 3) two supra-intestinal trunks, (4, 5) two lateral or 
“intestino-tegumentary,” and finally, (6) one ventral supra-nervian vessel. 
This system differs from that of any other Oligocheetous worm by the presence 
of two supra-intestinal vessels, but with this exception conforms to the ordinary 
type, being very similar in its general arrangement to Pericheta, Urochwia, and 
Pontodrilus. 'The dorsal vessel lies on the dorsal side of the alimentary canal, 
in actual contact with it in the anterior and posterior portions; it is only in 
the region which lies between the 8th and 16th segment, that the dorsal vessel 
lies well above the alimentary canal, as shown in Plate XX VI. figs. 1, 2, which 
represent diagrammatic vertical sections through the body of the worm in this 
region. The dorsal vessel takes its origin from a capillary network on the 
anterior part of the pharynx, and has the remarkable peculiarity of not remain- 
ing a single uniform tube in its course backwards, but bifurcates no less than 
five times in the first eight segments, the bifurcations always coalescing again 
directly ; this is shown on Plate X XV. fig. 2. The dorsal vessel gives off one or 
two branches in the anterior segments, and in the 8th, 9th, 10th, 11th, 12th, and 
13th gives off a branch on either side, which unites it directly to the ventral 
trunk ; these arches increase in size from before backwards, and the four last, 
which are the stoutest, are no doubt contractile, and function as “hearts.” The 
moniliform character of these vessels described in other worms is very con- 
spicuous here in the pairs occupying the 10th, 11th, 12th, and 13th segments ; 
the two pairs anterior to these are much slighter, and before joining the ventral 
vessel give off on either side a trunk (Plate XXV. fig, 4, 5), which in the case of 
the posterior one, at least, gives off another branch perforating the mesentery 
behind (Plate X XVI. fig. 2, ~). In the 7th segment, another pair of branches 
