254 THE VITAL FUNCTIONS. 



vessels are seen pursuing a slightly serpentine 

 course.* 



The tribe of JLumhrici, which includes the 

 earth-worm, is distinguished from the annelida 

 already noticed, by being more highly organized, 

 and possessing a more extensive circulation, and 

 a more complicated apparatus for the per- 

 formance of this function. The greater extent 

 of vascular ramifications appears to require in- 

 creased powers for carrying the blood through 

 the numerous and intricate passages it has to 

 traverse ; and these are obtained by means of 

 muscular receptacles, capable, by their succes- 

 sive contraction, of adding to the impulsive force 

 with which the blood is driven into the trunks 

 that distribute it so extensively. These muscu- 



* Duges represents the blood of this animal as moving in 

 different directions in the right and in the left lateral vessels ; 

 generally 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 curious to 

 find an example of a similar transverse circulation, in the 

 vegetable kingdom; this has recently been observed by Mr. 

 Solly and Mr. Varley, in a sprout of the Chara vulgaris, near 

 the end of which the enclosed fluid revolves continually on 

 its own axis, instead of following the ordinary course of ascent 

 and descent along the sides of the cylindric cavity. — See Trans, 

 of the Society of Arts, xlix. 180. 



