74 



THE VITAL FUNCTIONS. 



a general diffusion, or circulation of nourishment 

 through numerous channels of communication, into 



which certain absorbing vessels convey it from a 

 great number of external orifices, or mouths, as 

 they may be called. This is the case with the 

 Tania, or tape worm, which is composed of a series 

 of flat jointed portions, of which two contiguous 

 segments are seen, highly magnified, in Fig. 247, 

 exhibiting round the margin of each portion, a circle 

 of vessels (v), which communicate with those of the 

 adjoining segments ; each circle being provided 

 with a tube (o), having external o'^enings for im- 

 bibing nourishment from the surrounding fluids. 

 Although each segment is thus provided with a 

 nutritive apparatus complete within itself, and so 

 far, therefore, independent of the rest, the indi- 

 viduality of the whole animal is sufficiently deter- 

 mined by its having a distinct head at one extre- 

 mity, provided with instruments for its attachment 

 to the surfaces it inhabits. 



The Hydatid (Fig. 248) is another parasitic worm 

 of the simplest possible construction. It has a head 

 (o), (of which H is a magnified representation,) 

 furnished with four suckers, and a tubular neck. 



