$ 157. THE ANNELIDES. 169 
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 Chaetopodes 
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. 
4 The irregularity of the blood-currents has, un- 
-doubtedly, given rise to the numerous different 
opinions upon the circulation of these animals ; see 
Duges, Ann. d.Sc. Nat. XV. 1828, p. 308 ; Weber, 
in Meckel’s Arch. 1828, p. 899 ;_ Muller, Ibid. p. 
2435 and in Burdach’s Physiol. IV. 1832, p. 143 ; 
and Wagner, Isis, 1832, p. 635. If the valves 
which Leo'(Muller’s Arch. 1825, p. 421, Taf. XI. 
fig. 9) 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 Sanguisuga, Haemopis, Pontobdella, 
Nephelis, Piscicola, and others, the blood.is red ; 
it is colorless with some Clepsine, according to Fi- 
Nippi (Lettera sopra l’Anat. e lo sviluppo delle Clep- 
sine, 1839, Pavia, p. 11); it is also brown, violet or 
wed, according to the species. He also declares (loc. 
cit. p. 8), that with Clepsine and Piscicola, which 
dive wholly upon the blood of the lower animals, the 
*[§ 157, note 4... The memoir of Gratiolet 
(Mem. sur. POrganisation du systéme vasculaire de 
la Sangsue médicinale et de l’Aul vorace, pour 
servir & Phistoire des mouvements du sang dans les 
Hirudinées bdelliennes, in extract in the Comp. 
“Rend, 1850, XXXI. p. 699), is worthy of a special 
ireforence 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 Dugés, Weber and Miller, and their contained 
‘blood moves in a circular manner, sometimes one 
“way, sometimes the opposite. 
“The branches given off by these lateral vessels 
care of two kinds : 
‘A. Those destined for the skin, and which are 
ramified in the respiratory net-works ; they never 
anastomose with those of 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 
amuciparous vesicles. 
“tAll these branches arise from the branches or the 
Jarge arches which form a free anastomosis between 
15 
With the smal] Lumbricini, these are usually 
vascular system communicates directly through 
small canals with the coeca of the digestive canal, 
so that the contents of this last may pass into the 
blood without being changed. f 
6 See Henle, in Muller’s Arch. 1837, p. 83, Taf. 
VI. fig. 5 (Enchytraeus), and Hoffmeister, De 
vermibus quibusdam, &c., loc. cit. p. 14, Taf. Il. fig. 
4 (Saenuris variegata). 
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. 27; Dugeés 
Ann. d. Se. 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. 
8 The transverse anastomoses are simple with 
Lumobricus, but torose with Saenuris ; see Hoff- 
meiste?, 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. 
“This circulation, very different from that which 
Duges admits in the alleged pulmonary vesicles, 
shows how various are the means employed hy 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-Tandon, loc. cit. 
p. 183, Pl. X. fig. 10, 15, 16, and Pl. XII, fig. 13. 
—Ep. 
+ [§ 157, note 5.] The recent observations of 
Leydig (loc. cit. p. 119), have shown the blood of 
Piscicola tobe always colorless. This view is proba- 
- bly the correct one, since it better accords with the 
histological relations of the blood of these animals. 
— Ep. 
