254 WILLIAM BLAXLAND BENHAM. 
The dorsal trunk is always muscular. It may be simply 
tubular in Lumbricus, Moniligaster, Pericheta, Ti- 
tanus, and others, or it may be ampullate and valvular, as 
in Urocheta throughout the body; or tubular posteriorly 
and ampullate anteriorly as in Anteus; in both these last 
forms:the dorsal trunk is bent to one side in a loop, just before 
the region where it gives off the lateral hearts. 
In Pleurocheta the dorsal trunk divides in some of the 
anterior somites to form a double vessel, the halves of which 
unite again ; there appears also to be a second dorsal vessel below 
the large contractile trunk. Beddard (40) has described a 
somewhat similar arrangement in a species of Acantho- 
drilus and in Microcheta. 
Longitudinal lateral trunks appear at each side of the 
alimentary tract anteriorly in some worms. In Lumbricus 
these are formed by a branch from the dorsal trunk on each 
side in somite x. In Urocheta and Pontodrilus [and in 
Microcheta] (and doubtfully in Pleurocheta) they spring 
from a network in a part of the alimentary tract and run 
through eight or nine somites to the pharynx. 
The lateral hearts usually occupy the somites in which 
the seminal reservoirs are, and those just anterior to them. 
In Urocheta and Anteus there are three pairs, in somites 
VIII, 1x, xX; in Plutellus, in somites x, x1, x11; in Rhino- 
drilus, in somites xvi1, xvilI, x1x; whilst in Lumbricus, 
Digaster, and Titanus, they exist in somites vi1r to x11; in 
T. forguesii, in somites x1, x11, the hearts communicate with 
dorsal and typhlosolar trunks. In Pleurocheta and Peri- 
cheta the lateral hearts are in somites x to xt, and in 
Pontodrilus they are in somites v to x1. These lateral 
hearts pass from the dorsal to the ventral trunk, but other 
vessels exist in some forms, passing from the typhlosolar to the 
ventral trunk. These “intestinal hearts” are present in 
somites xx, xx1, xx11 in Rhinodrilus just behind the lateral 
hearts, and in Urocheta in somites xi and xiv; in this 
latter worm they are very much larger than the lateral 
hearts, whilst in Pontodrilus the two intestinal hearts 
