198 



ANNELIDA. 



cular loop (b) derived from the lateral vessel itself (a), which ter- 

 minates by ramifying upon the vesicle f, in a similar manner. The 



Fig. 81. 



walls of the loop &, are extremely thick and highly irritable ; but, 

 on tearing it across, the internal cavity or canal by which it is 

 perforated is seen to be of comparatively small diameter, so that we 

 are not surprised that, although such appendages to the respira- 

 tory sacs were detected and well delineated by former anatomists,* 

 their nature was unknown, and they were supposed to be glandular 

 bodies appropriated to some undiscovered use. From the ar- 

 rangement above described, it is evident that small circular cur- 

 rents of blood exist, which are independent, to a certain extent, of 

 the general circulation ; since opposite to each membranous bag a 

 portion of the fluid contained in the lateral vessel (a) is given off 

 through the muscular tube (&), which thus resembles a pulmonary 

 heart, and after being distributed over the walls of the respiratory 

 vesicle, and in this manner exposed to the influence of oxygen, 

 the blood returns into the general circulation. 



(240.) The nervous system of the leech (Jig. 80, 2, k) consists of 



* Delle Chiaje, op. cit. Moquin Tandon, Monographic sur la famille des Iliru- 

 dinees, 4to. Montpellier, 1827. 



