184 THE VITAL FUNCTIONS. 



is distinguished from the annelida already noticed, by being 

 more highly organized, and possessing a more extensive cir- 

 culation, and a more complicated apparatus for the perform- 

 ance of this function. The greater extent of vascular rami- 

 fications appears to require increased 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 successive contraction, of add- 

 ing to the impulsive force with which the blood is driven 

 into the trunks that distribute it so extensively. These mus- 

 cular appendages are globular or oval dilatations of some of 

 the large vascular trunks, which bend round the sides of the 

 anterior part of the body, and establish a free communication 

 between the dorsal and the abdominal vessels. They are 

 described by Duges as consisting, in the Lumbricus gigas, 

 of seven vessels on each side, forming a series of rounded 

 dilatations, about twelve in number, resembling a string of 

 beads.* 



In the Lumbricus terrestris, or common earth-worm, 

 there are only five pairs of these vessels; they have been de- 

 scribed and figured by Sir E. Home:f but the most full and 

 accurate account of their structure has been given by Mor- 

 ren, in his splendid work on the anatomy of that animal.J 

 Fig. 349, which is reduced from his plates, represents these 



* They are termed by Duges, Valsseaux moniliformes, ou dorso-dbdomi- 

 naux. Annales des Sciences Naturelles, xv. 299. 



f Pbilos. Transact, for 1817, p. 3: and PI. iii. Fig-. 4. 



+ " De Lumbrici terrestris Historia naturalis, necnon Anatomia Tractalus." 

 Qto. Bruxelles, 1829. 



