ANNELIDA TERRICOLA. 



proof that the nourishment of animals was not exclusively 

 derived from animal and vegetable substances, since in this 

 case they supposed nutriment to be obtained from matter be- 

 longing to the mineral kingdom. This supposition, however, 

 has been long since exploded, for it is not from the earth that 

 nourishment is afforded, but from the decaying animal and 

 vegetable particles mixed up with the soil taken into the 

 stomach ; so that the exception to the general law of nature 

 supposed to exist in the earth-worm, has no foundation in 

 truth. The whole intestinal tract of one of these animals 

 consists of a wide oesophagus, which terminates in a crop-like 

 dilation ; to this succeeds a muscular gizzard, and a long sac- 

 culated intestine, which passes in a direct line to the anus. 



The circulation of the blood in the terricolous Annelidans 

 has been the subject of much discussion, and until recently 

 was but very imperfectly understood. In the earth-worm 

 there are three principal trunks connected with the vascular 

 system. First, a dorsal vessel runs along the whole length of 

 the back, in close contact with the intestine, upon which it lies ; 

 this vessel is tortuous, and exhibits constant movements of 

 contraction and dilatation, by which the blood is propelled in 

 continuous undulations from the tail towards the head. Two 

 other large vessels occupy the ventral region of the body ; of 

 these, one, which we shall call the ventral vessel, runs immedi- 

 ately beneath the alimentary tube ; while the other, which is 

 situated close under the skin, and consequently beneath the 

 ventral chain of ganglia composing the nervous system, by 

 which it is separated from the last, may be distinguished as 

 the sub-ganglionic vessel. These three great trunks are united 

 by important branches, and form two distinct systems ; one 

 of which is deeply seated, being distributed to internal vis- 

 cera ; the other is superficial, giving off innumerable vessels to 

 the integuments of the body, which, by ramifying through the 

 skin, form an extensive vascular surface adapted to respiration. 



The ventral vessel, like the dorsal, may be traced quite to 

 the anterior extremity of the worm, where numerous small 

 anastomosing branches unite the two trunks; but these inos- 

 culations are of little consequence in describing the circular 

 movement of the blood, a more important communication 

 being established, through which the blood passes freely from 

 one to the other, by the intervention of seven or eight pairs of 

 large canals, situated in the immediate neighborhood of the 



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