CIRCULATION IN THE ANNELIDA. 



1S3 



(Fig. 347;) where a is the anterior, and p the posterior ex- 

 tremity of the animal, the dorsal vessel occupying the mid- 



dle straight line between the two lateral vessels, and the di- 

 rection of the stream in each being indicated by the adjacent 

 arrows. The blood in the abdominal vessel following the 

 same course as that in the dorsal vessel, the same diagram 

 represents also these vessels seen from below. Fig. 348 is 

 an inferior view of the Erpobdella, showing the numerous 

 ramifications of the abdominal vessel; the lesser branches 

 encircling the nervous ganglia, and accompanying the prin- 

 cipal nervous filaments which proceed from them: while the 

 lateral vessels are seen pursuing a sliglitly serpentine 

 course.* 



The tribe of Lumbrici, which includes the earth-worm, 



♦ Duges represents the blood of this animal as moving- in different direc- 

 tions in the rig-ht and in tlie left lateral vessels; g-enerally backwards in the 

 former, and forwards in the latter: at the same time that it moves backwards 

 in the dorsal, and forwards in the abdominal vessel. In the communicating 

 branches which pass transversely from one lateral vessel to the other, the 

 blood flows from left to right in those situated in the anterior half of the 

 body, and from right to left in those of the posterior half: so that the plane 

 in which its circuit is performed is horizontal, instead of vertical. It is curi- 

 ous to find an example of a simiUu* transverse circulation, in the vegetable 

 kingdom; this has recently been observed by Mr. Solly and Mr. Vai-ley, in a 

 sprout of the Chara vulgaris, near the end of which the enclosed fluid re- 

 volves continually on its own axis, instead of following the ordinary course 

 of ascent and descent along the sides of tlic cylintkic cavity.— Sec Trans, of 

 the Society of Arts, xlix. 180. 



