ANELLATA. 137 



each of these swellings a transverse branch is sent off to either 

 side (f,/), and from the seventh to the fifteenth ganglionic sinus a 

 second pair of transverse vessels of smaller size is given off', just be- 

 hind the ganglionic sinus. 



The respiratory function would seem to devolve partly upon the 

 tegumentary capillaries, and partly upon those capillaries which spread 

 upon the mucous sacculi. These latter capillaries are not, however, 

 more numerous than those of the other organs of the body. The 

 more important office of the sacculi would seem to be as the 

 recipients of the secretion of peculiar loop-shaped glands, which 

 they receive by a very short and slender duct. There are seventeen 

 pairs of these mucous glands i^figs. 71, 72. g., g\ the five posterior of 

 which lie on each side the long terminal gastric sacculi, and the rest 

 in the interspaces of the shorter caeca. Each gland pours its se- 

 cretion into a circular sac {Jigs.l^, 12. h, h^, which opens exter- 

 nally (^Jig.1\. i, i) upon the skin. These dermal pouches have com- 

 monly been described as the respiratory organs ; they are evidently 

 analogous in their position to the respiratory organ of the higher 

 Articulata ; but in function they seem to be reduced to supplying 

 the skin with its abundant mucous secretion, and the ova with their 

 cocoon-like coverings at the season of generation. 



Morren has minutely described the circulating system of the earth- 

 worm ; in a species of which (Lumbricus variegatus) Bonnet * saw 

 the red blood propelled forward by the systole and diastole of the 

 dorsal vessel towards the head, and noticed its accelerated course near 

 that part. 



In the tubicolar anellides, according to Dr. M.Edwards f, the dorsal 

 contractile artery is unusually short. In the Terebella it receives nu- 

 merous veins from the intestine, and a large accession of the circu- 

 lating fluid from two wide transverse venous trunks, which encircle 

 the commencement of the intestine, and which receive recurrent veins 

 from the oesophagus, also a small vein from the integuments of the 

 back. This short dorsal vessel is, in fact, the general receptacle of 

 the venous system, and, by its function, it represents a pulmonic 

 heart. It transmits the venous blood almost exclusively to the ce- 

 phalic branchiae by three pairs of branchial arteries, which arise from 

 its anterior extremity. The oxygenated blood is returned by the 

 branchial veins to a large ventral trunk, situated immediately above 

 the ganglionic nervous chord. This vessel supplies a pair of trans- 

 verse branches to each ring of the body, which distribute filaments 

 to the integuments and the feet, and then ascends to supply the intes- 



* Observations sur les Vers, CEuvres, i. p. 121. 



f Sur la Circulation dans les Anellides, Annales des Sciences, Nat. X. p. 193. 



