cxxiv Introduction. 



The digestive canal in Vermes wlien present resembles their ex- 

 ternal tegumentary system in being homonomous except in its 

 anterior portion. In this part of the tract we often find a muscular 

 protrusible and dentigerous oesophagus; the stomach is by no 

 means always differentiated from the intestine, and the segments 

 which intervene between the oesophagus and the short often upward 

 turning rectum^ may be conveniently called ' gastro-ileal/ It may 

 take a simple antero-posterior course^ or it may have lateral diver- 

 ticula of very various degrees of complexity developed upon it. 

 It is seldom convoluted. The salivary glands are usually^ and the 

 hepatic are always represented merely by layers of cells impacted in 

 the walls of the digestive tube. 



Many Vermes possess an extensive vascular system, which, 

 however, as containing usually a coloured, but not a corpusculated 

 fluid, is called a ' pseudhaemaF system, and is to be considered respi- 

 ratory in function. The corpusculated nutritive true blood is con- 

 tained usually in the perivisceral cavity alone ; in a few instances 

 it has been found to penetrate into the so-called pseudhaemal 

 vessels. Specialized respiratory organs are rarely found in Vermes ; 

 the possession of a j)eculiar depuratory apparatus is characteristic 

 of the entire Sub-kingdom. This system appears to stand in a 

 complementary relation to the branchial ; being largely develojied 

 where, as in the OUgochaeta and parasitic worms, that system 

 fails to be developed, on account of the medium in which those 

 animals live ; and being reduced to comparative insignificance in 

 the marine Polyclmeta^ where the branchiae are so prominent a 

 feature in their organization as to have gained for them the name 

 of ' Branchiata.^ In the non-segmented worms these organs are 

 known as the ' water- vascular^ system ; and they take the shape 

 of two bilaterally symmetrical tubes, opening by one or two orifices 

 on the external surface of the body, and ramifying abundantly in 

 its interior. In the segmented Vermes or Annulata, these organs 

 are known as ^ segmental organs ; ' and may be repeated in nearly 

 every segment of the body. In most Vermes the internal terminal 

 segments of these tubes aj^pear to be clothed with cilia ; the seg- 

 ments in more immediate connection with the exterior outlet are very 

 ordinarily possessed of much thicker, glandular, and contractile 

 walls. In the Annulata, with a few exceptions, the inward pro- 

 longations open by infundibuliform orifices into the perivisceral 



