§157. 



THE ANNELIDES. 



1G9 



sometimes backwards and oscillates from one side to the other, through the 

 transverse vessels/^' With most genera, the blood is red, being colorless 

 with a few only, and it is always poor in corpuscles.'^* The Chaetopodcs 

 have no lateral vessels. Their circulation is often due to pulsatory organs, 

 and there is a great variety in the disposition of their vascular trunks and 

 sinuses. 



With the Abranchiati, the dorsal vessel lies close upon the intestinal 

 canal, and is almost wholly enveloped in the hepatic tissue. At the ante- 

 rior extremity, it divides in many bifurcating branches, which, after encom- 

 passing the pharynx, unite below it, and form the ventral vessel.'*^' This 

 vessel accompanies the ventral cord to the posterior extremity, and connects 

 with the dorsal vessel by bifurcating branches, as before.'''' The transverse 

 anastomoses connecting the dorsal and ventral vessel, form at each segment 

 simple, or torose canals.^*" With the small Lumbricini, these are usually 



4 The irreiiularity of the blood-currents has, un- 

 doubtedly, given rise to the numerous different 

 opinions upon the circulation of these animals ; see 

 Dufces, Ann. d. Sc. Nat. XV. 1828, p. 308 ; WeOer, 

 in Meckel's Arch. 182S, p. 399 ; Miiller, Ibid. p. 

 24 ; and in Burdach's Physiol. IV. 1832, p. 113 ; 

 and fVazner, Isis, 1832, p. 635. If the valves 

 which Leo {Miiller's Arch. 1825, p. 421, Taf. XI. 

 fig. 9)k has found in the dorsal and ventral vessels 

 of Piscicola, should be found also with other Hiru- 

 dinei, it would throw some light upon the real course 

 of the circulation.* 



5 With Sanf^uisuga, Haemopis, Pontobdella, 

 Nephelis, Piscicola, and others, the blood is red ; 

 it is colorless with some Clepsine, according to Fi- 

 lippi (Lettera sopra 1' Anat. e lo sviluppo delle Clep- 

 sine, 1839, Pavia, p. 11) ; it is also brown, violet or 

 red, according to the species. He also declares (loc. 

 cit. p. 8), that with t'lepsine and Piscicola, which 

 live wholly upon the blood of the lower animals, the 



* [§ 157, note 4."^ The memoir of Gratiolet 

 (Mem. sur. I'Organisation du systeme vasculaire de 

 la Sangsue m^dicinale et de I'Aulostome vorace, pour 

 Bervir d I'histoire des mouvements du sang dans les 

 Ilu'udinees bdellieunes, in extract in the Comp. 

 Rand. 1850, XXXI. p. 639), is worthy of a special 

 refin-ence in this connection. He says : " The lat- 

 eral vessels, whose walls are very muscular, are 

 the principal organs for the movement of the blood; 

 they contract alternately, as has been well observed 

 by Dugis, JVeber and Mailer, and their contained 

 blood moves in a circular manner, sometimes one 

 way, sometimes the opposite. 



" The branches given off by these lateral vessels 

 are of two kinds : 



" A. Those destined for the skin, and which are 

 ramified in the respiratory net-works ; they never 

 anastomose with those ^f the opposite side. Before 

 their final and minute ramifications, they form a 

 large varicose net-work under the skin, which hith 

 erto has been regarded as a plexus of hepatic ves- 

 sels, but which is positively an interlacement of 

 blood-vessels. 



" B. The other branches are destined for the 

 small intestine, and its spiral valve for the testicles, 

 the copulatory apparatus, to the loops and to the 

 muciparous vesicles. 



'•AH these branches arise from the branches or the 

 large arches which form a free anastomosis between 



15 



vascular system communicates directly through 

 small canals with the coeca of the digestive canaj, 

 so that the contents of this last may pass into the 

 blood without being changed.! 



6 See Henle, in Mxiller's Arch. 183T, p. 83, Taf. 

 VI. fig. 5 (Enchytraexis), and Hqff'meister, De 

 vermibus quibusdara, &c., loc. cit. p. 14, Taf. II. fig. 

 4 {Saenuris variegata). 



1 With Lumbricus, there are, beside the princi- 

 pal ventral vessel, three others smaller, and in di- 

 rect connection with the ventral cord. Two of these 

 pass off laterally, and the third underneath ; see 

 Leo, De Structura Lumbrici terrestris, p. 2'i\ Dug is 

 Ann. d. Sc. Nat. XV. 1828, p. 298; and Morren, 

 loc. cit. p. 152, Tab. XXI.-XXIV. fig. 5, who 

 especially has carefully described the vascular sys- 

 tem of Lumbricus terrestris. 



S The transverse anastomoses are simple with 

 Lumbricus, but torose with Saenuris ; see //o^- 

 meister, loc. cit. 



the two lateral vessels. The consequences of this 

 form of structure may be easily summed up. The 

 blood oscillates from the alternate contractions 

 from one pulmonary net-work to another. It circu- 

 lates in the principal organ of the intestinal ab- 

 sorption, in the testicles, and in the muciparous 

 glands. J, 



" This circulation, very different from that which 

 Dugis admits in the alleged pulmonary vesicles, 

 shows how various are the means employed by na^ 

 ture. Here she determines the course of the blood 

 by means of valves and stoppers ; while elsewhere 

 she accomplishes the same end by causing certain 

 blood-currents to prevail over others." 



The valvular structure of the vessels with Pisci- 

 cola, as mentioned by Leo, has since been con- 

 firmed by Leydig (loc. cit.), who has found it also 

 with Clepsine. Leydig calls the attention to 

 another kind of circulatory system in Piscicola ; 

 see loc. cit. p. 116. But this point has not yet been 

 well made out ; see also Moquin-Tandoriy loc. cit. 

 p. 133, PI. X. fig. 10, 15, 16, and PI. XU, fig. 13. 

 —Ed. 



t [ § 157, note 5.] The recent observations of 

 Leydig (loc. cit. p. 119), have shown the blood of 

 Piscicola to be always colorless. This view is proba- 

 bly the correct one, since it better accords with the 

 histological relations of the blood of these animals. 

 — Ed. 



