ANATOMY AND HISTOLOGY OF PLEUROCH ATA MOSELEYI. 497 
very extended, D’UpExkem,* LANKESTER,t and CiapArnDE{ have made us 
thoroughly acquainted with these organs in Lumbricus, PERRIERS has 
increased our knowledge enormously with respect to the three genera, Ponto- 
drilus, Urocheta, and Pericheta; to the last genus also VAILLANT || and 
Horst * have added details of considerable importance ; but of the circulatory 
organs in the many interesting genera described by PERRIER in the Mémoires 
du Muséum, owing to their bad state of preservation, not much could be 
asserted with confidence. It would be useless, therefore, with the comparatively 
scanty materials that we have at hand, to attempt to generalise ; on the whole, 
in the number and character of the main trunks of the vascular system, 
Pleurocheta seems to stand midway between the Ante-clitellians, ¢9., the 
common earthworm, on the one hand, and the Intra and Post-clitellians on the 
other, with rather more affinities to the latter groups, but no more special 
relationship to any particular genera among those which compose these two 
somewhat heterogeneous groups can be made out. 
The vascular system in the Oligochwta, as far as we know it, contrary to 
what we might expect from the analogy of other groups of animals, does not 
form a good basis for classification. The main trunks are constant through so 
many and so widely different genera, and the number and position of the 
hearts, which might at first sight seem likely to be useful in this direction, 
vary in the most capricious manner from one species to another; for example, 
in Pericheta cingulata, described by VAILLANT,** there are three pairs of 
hearts, and in a Perichwta described by Horst,t{} there are in all six pairs of 
hearts, and one unpaired half-arch. Among the various species of Pericheta 
described by PeErriER, the same variations are observable—‘‘l’appareil circu- 
latoire possede une grande variabilité qui ne semble guere autoriser l’employer 
dans une caractéristique.” 
To resume the account of the vascular system of Plewrochwta; in the 11th, 
12th, and 13th segments the hearts, connected as in the other segments with 
the dorsal vessel, give off two branches directly after issuing from it, the 
posterior one is distributed to the mesentery behind, and the anterior one to 
the walls of the alimentary canal; the mesenteric branch appears to be given 
off in the other segments anterior to the 11th, but not the intestinal, at least it 
was not visible in either of the specimens dissected. From the supra-intestinal 
* D’Upekem, Nouv. Mém. de V Acad. Roy. Bruz., t. xxxv., 1865. 
{ Lanxester, “On the Anatomy of the Earthworm,” Quarterly Journal of Microscopical Science, 
1864-65. 
{ Cuapargpg, loc. cit. 
§ PrrRieR’s numerous memoirs already cited. 
|| Varnuant, loc. cit. {| Horst, loe. cit. 
** Variant, loc. cit. ++ Horsv, loc, cit. 
{tt Perrier, Nouvelles Archives du Museum, p. 26. 
VOR SX. PART II. 4H 
