§ 156. THE ANNELIDES. 167 



of (he intestinal canal ; these are narrow and their botrjoidal extremities 

 lie in the interstices of the dorsal wall of the body. 



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. 



CIKCULATOEY 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. 



AVith 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, Trcviranus, Milne Edwards, XXIX. A. fig. 28, 29. With many, this hepatic 



loc. cit., and Grube, loc. cit. p. 54. layer envelops also the bloorl-vessel upon the dorsal 



» Accoidin,!; to Henle (Mu/ler's Arch. 1837, p. surface of tlie intestine. It is possible that tlie 



81, Taf. VI. hg. 2), this glandular envelope forms a yellow canal described by Morren, with Lumbri- 



villous envelojie about the intestine. This is also cus terrestris as Chloragogena, is only tliis hepat- 



true of Lumbrictis, Liimbriculus, Nais, and ic mass (loc. cit. p. 143, Tab. XV. XVI.). Another 



Chaetogaster. The glandular sacs are greenish canal which is traversed by blood-vessels and closed 



with Branchiobdella {Henle, loc. cit. 1835, p. 575), at both extremities, and which is contained in a 



yellowish with Amphitrite {Rtithki, Danzig, longitudinal enlargement upon the internal sur- 



Schrift. loc. cit. p. 65). With Sangiiuu^a, the ex- face of the intestinal canal, and is called by Mor- 



cretory ducts of the hepatic sacs inter-anastomose ren, Tyjihlosolis (loc. cit. p. 138, Tab. XI. XII. 



and form a kind of net-work around the stomach XVI. XVII.) may perhaps be regai-ded as a rocep- 



and its coeca ; see Brandt, Med. Zool. p. 247, Taf. tacle of chyle.* 



* [ § 155, note 8.] The hepatic organs with the (Lumbricus, Nais), and the long, thread-like and 



Annelides have been successfully studied by JVill coecal glands {Hirudo, Haemopis, Auiaco.iloma, 



(Muller's Arch. 1843, p. 508), who has used chem- Helluo, Piscicola, Clepsine) which surround the 



leal tests, lie has found the glandular layer intestinal canal, to be organs of tliiu nature. — Ed. 



