ANNELIDA. 195 



tives of the wide pouches met with in the leech are narrow and 

 branched tubes terminating in blind extremities, to which it is 

 usual to assign the office of separating a biliary secretion ; and, 

 according to this view, we may regard the caeca of the leech as the 

 simplest rudiments of the assistant chylopoietic glands, the first 

 pair (g, g) 9 from their proximity to the mouth, may be destined 

 to furnish a salivary fluid, and the succeeding ones to perform the 

 functions of biliary follicles. 



The small size of the intestine (e), when compared with the 

 capacious stomach described above, is remarkable : it commences 

 by a minute orifice from the termination of the digestive cavity, 

 and becoming slightly enlarged passes in a straight line, lodged 

 between the two posterior cseca, to the anus, which is an almost 

 imperceptible aperture placed at the root of the posterior sucker ; 

 four small and apparently glandular masses are appended to this 

 short canal, but their nature is unknown. The entire alimentary 

 apparatus is retained in situ by numerous membranous septa, 

 (m, w,) passing between its outer walls and the muscular parietes 

 of the body. 



(237.) It has already been mentioned, that, in the abranchiate 

 Annelidans, the organs provided for respiration are a series of 

 membranous pouches, communicating externally by narrow ducts or 

 spiracles, as they might be termed, into which aerated water is 

 freely admitted. These respiratory sacculi, in the leech, are about 

 thirty-four in number, seventeen being visible on each side of the 

 body : they are extremely vascular ; and in connection with every 

 one of them there is a long glandular-looking appendage, repre- 

 sented in the figure, (Jig. 80, 2, m,) that was looked upon until 

 recently as being intended to furnish some important secretion, 

 but which recent discoveries have shown to be connected with the 

 propulsion of the blood over the walls of the breathing vesicle, in a 

 manner to be explained immediately. It would seem, however, that 

 the respiratory function is not exclusively carried on by the agency 

 of the lateral sacculi : the entire surface of the body is permeated 

 by innumerable delicate vascular ramifications ; and, from the thin- 

 ness of the integument, it is evident that the blood which tra- 

 verses the cutaneous net-work thus extensively distributed must 

 be more or less completely exposed to the influence of oxygen 

 contained in the surrounding medium ; nay, it would even appear 

 from careful examination of the movements of the blood, as seen 

 in the transparent bodies of some of the Hirudinidte, that a kind 



o % 



