§ 156. THE ANNELIDES. 167 
of the intestinal canal ; these are narrow and their botryoidal extremities 
lie in the interstices of the dorsal wall of the hody. 
With Aphrodite aculeata, the structure is analogous but differs in that 
these appendages have more the aspect of coeca with thin walls, and have 
not the ramified diverticula except in their central part and between the 
already-mentioned saccular dilatations.” 
As an hepatic organ may be regarded with more certainty a particular 
tissue colored in part brownish yellow, and partly greenish yellow, which 
closely surrounds the whole intestinal canal of most Annelides. Carefully 
examined, this tissue is found composed of closely-aggregated glandular 
sacs which empty their contents into the intestine either directly, or by 
many common excretory ducts. This contained liquid is, with most 
species a transparent fluid in which are suspended brown granules, and it 
resembles the bile of the higher animals. 
CHAPTER VI. 
CIRCULATORY SYSTEM. 
§ 156. 
This system is highly developed with the Annelides. The blood is usu- 
ally colored, and the vascular system, remarkable for many peculiarities, 
is complete and closed. 
This system may be divided into a central and a peripheric part. 
The first consists of large contractile vessels taking the place of a 
Heart. There are also various heart-like organs in the shape of varicose 
dilatations upon the course of the contractile vessels. The principal ves- 
sels have a longitudinal course, occupying the whole length of the median 
line of the body, — one as a dorsal, and the other as a ventral vessel. 
With many Hirudinei, there are also lateral vessels. The dorsal and 
ventral vessels unite at both extremities, beside anastomosing by transverse 
branches in the separate segments. 
When there are lateral vessels, these also connect with the median ves- 
7 See Pallas, Treviranus, Milne Edwards, 
loc. cit., and Grube, loc. cit. p. 
8 According to Henle (Muller's Arch. 1837, p. 
81, Taf. VI. fig. 2), this giandular envelope forms a 
villous envelope about the intestine. This is also 
true of Lumbricus, Lumbriculus, Nais, and 
Chaetogaster. The glandular sacs are greenish 
with Branchiobdella (Henle, loc. cit. 1835, p. 575), 
yellowish with Amphitrite (Rathkée, Danzig. 
Schrift. loc. cit. p. 65). With Sanguisuga, the ex- 
cretory ducts of the hepatic sacs inter-anastomose 
and form a kind of net-work around the stomach 
and its coeca ; see Brandt, Med. Zool. p. 247, Taf. 
* [§ 155, note 8.] The hepatic organs with the 
Annelides have been fully studied by Will 
(Miller's Arch. 1848, p. 508), who has used chemm- 
ical tests. He has found the glandular layer 
. 
XXIX. A. fig. 28, 29. With many, this hepatic 
layer envelops also the blood-vessel upon the dorsal 
surface of the intestine. It is passible that the 
yellow canal described by Morren, with -Lumbri- 
cus terrestris as Chioragogena, is only this hepat- 
ic mass (loc. cit. p. 142, Tab. XV. XVI.). Another 
canal which is traversed by blood-vessels and closed 
at both extremities, and which is contained in a 
longitudinal enlargement upon the internal sur- 
face of the intestinal canal, and is called by Mor- 
ren, Typhlosolis (loc. cit. p. 138, Tab. XI. XII. 
XVI. XVII.) may perhaps be regarded as a recep- 
tacle of chyle.* 
(Lumbricus, Nats), and the long, thread-like and 
coecal glands (Hirudo, Haemopis, Auiacostoma, 
Helluo, Piscicola, Clepsine) which surround the 
intestinal canal, to be organs of this nature. — Ep. 
