210 THE ANATOMY OF INVERTEBRATED ANIMALS. 



which appear to represent branchiae, may be discovered on 

 the dorsal side of the bases of the parapodia, at any rate, in 

 young specimens. In some species of Polynoe the parapodia 

 give rise, at corresponding points, to large, richly ciliated, 

 malleiform tubercles, in which the caeca of the alimentary 

 canal terminate. In Sigalion, a filiform, ciliated branch ia 

 depends from the upper part of the somite, beneath the ely- 

 tron ; and, besides this, curious little ciliated palettes are 

 arranged upon the dorsal surface of the parapodia, and upon 

 the sides of the anterior somites. But the best-developed 

 branchiae among these Annelids are possessed by the Amphi- 

 nomidce, and the Eunicidw among the Errant ia ; the Tere- 

 bellicl'je, and the Ssrpulidoe among Ijie Tubicola. In the 

 three former families the branchiae are ciliated branched 

 plumes, or tufts, attached to the dorsal surface of more or 

 fewer of the somites. In the last (Fig. 54) they are exclu- 

 sively attached to the anterior segment of the body, and 

 present the form of two large plumes, each consisting of a 

 principal stem, with many lateral branches. The stem is 

 supported by a kind of internal skeleton, of cartilaginous 

 consistence, which sends off processes into the lateral branches. 



I have been unable to find any pseud-haemal vessels in 

 Polynoe squamata, and, as Claparede ' could discover none in 

 the transparent P. lunulata, it is safe to assume their non- 

 existence. Claparede, in fact, denies them to the whole of 

 the Aphroditidce. 



When it is present, the pseud-haemal svstem varies very 

 much in the arrangement of its great trunks ; but they com- 

 monly consist of one or two principal longitudinal dorsal and 

 ventral vessels, which are connected in each somite by trans- 

 verse branches. Where branchiae exist, loops or processes of 

 one or other of the great trunks enter them. The dorsal and 

 the ventral trunks are usually rhythmically contractile, and 

 contractile dilatations at the bases of the branchiae (Eunice), 

 in portions of the lateral trunks (Arenicola), or in those 

 which supply the proboscis (Eunice, Nereis), have received 

 the name of " hearts." The direction of the contractions is 

 usually such that the blood is propelled from behind forward 

 in the dorsal vessel, and in the opposite direction in the ven- 

 tral vessel ; but the course which it pursues in the lateral 

 trunks is probably very irregular. In CMorcema, in which 

 even the smallest ramifications of the vessels are contractile, I 



1 "Annelides Chetopodes du Golfe de Naples," 1868, p. 65. 



