444 SANGUIFEROUS SYSTEM. 



rous anastomoses among the principle sanguiferous trunks, 

 it is easy to perceive how the circulation in these animals 

 can 5 by the closing of the divided ends of the vessels, become 

 accommodated to extensive mutilations, and proceed without 

 interruption in a few segments detached from the trunk. 

 Some of the simpler forms, as stylaria, are thus enabled to 

 extend their means of propagation by the spontaneous trans- 

 verse division of their body. 



Besides the ordinary dorsal artery, extending forwards 

 between the fifteen pairs of ramose branchiae in the arenicola, 

 the great subgastric vein, and two smaller vessels extending 

 along the sides of the nervous columns, distinct longitudinal 

 gastric vessels^ one superior and one inferior, are seen ex- 

 tending along the alimentary canal, and forming delicate 

 plexuses on its parietes. The numerous branchial vessels 

 are observed to be connected directly with the great dorsal 

 and ventral trunks. As in most other annelides, enlarge- 

 ments, here one on each side, are formed at the anterior part 

 of the body, on the anastomosing branches between the great 

 superior and inferior median vessels, and these two sinuses 

 have been considered as the two auricles of the heart in this 

 animal cavities, however, which are not found co-existent 

 in the heart of animals lower than the amphibious vertebrata. 

 The arterialised blood from the ramified branchiee of the am- 

 phinome appears to be collected, as usual, into two longitudinal 

 lateral trunks, which convey it, by numerous anastomoses, 

 into the great advancing trunk of the dorsal vessel, before that 

 systemic artery turns downwards and backwards, to ramify on 

 the internal viscera ; and it is again collected from the system 

 into venous trunks, from which the branchial arteries convey 

 it to the respiratory organs. The same plan of the circulat- 

 ing system is seen in the leech, where the great median dor- 

 sal and median ventral trunks are extended along the whole 

 body, giving off numerous symmetrical branches on each side 

 in their course ; and two large lateral vessels follow along 

 the margins of the segments, receiving in their progress 

 regular alternating branches from the superior and inferior 

 parts of the body. The great ventral vein extended beneath 

 the alimentary canal, appears to be enlarged opposite to each 

 of the subjacent ganglia, and to encompass the nervous 

 columns by its numerous circles of anastomosing branches, 

 producing thus a hypo-neural as well as an epi-neural vein; 



