CIRCULATION IN THE CRUSTACEA. 185 



singular appendages to the vascular system of the earth- 

 worm, separated from their attachments, and viewed in con- 

 nexion only with the dorsal and abdominal trunks in which 

 they terminate. The abdominal vessel, (A, A,) on arriving 

 near the resophagus, is dilated, at the point B, into a globu- 

 lar bulb (c,) which is followed, at equal intervals, by four 

 others (c, c.) From each of these bulbs, or ventricles, as 

 they are termed by Morren, a vessel (D) is sent off at right 

 angles, on each side; this vessel also enlarges into several 

 nearly globular dilatations (E,) followed by a still larger, and 

 more elongated oval receptacle (F,) which completes the se- 

 micircular sweep taken by the vessel in bending round the 

 sides of the body, in order to join the dorsal vessel (G, G,) in 

 which all the other four communicating vessels, presenting 

 similar dilatations, terminate. Sir E. Home is of opinion 

 that these dilated portions of the vessel are useful as reser- 

 voirs of blood, for supplying it in greater quantity to the 

 neighbouring organs, as occasion may require: but Morren 

 ascribes to them the more important office of accelerating, 

 by their muscular action, the current of circulating blood. 

 If the latter of these views be correct, which the strong pul- 

 sations, constantly visible in these bulbs, render extremely 

 probable, this structure would offer the first rudiments of 

 the organ which, in all the superior classes of animals, per- 

 forms so important an office in the circulation of the blood, 

 namely, the heart: and this name, indeed, is given by Cu- 

 vier, Morren, and others, to these dilated portions of the 

 vascular systems of the higher orders of Annelida.* 



Here, also, the statements of different anatomists are at 

 variance, with regard to the direction taken by the blood 

 while circulating in the vessels: Home and Duges represent 

 it as proceeding forwards in the dorsal, and backwards in 

 the abdominal vessels; a course which implies its descent 



* It is remarkable that the blood in most of the Annelida has a bright 

 scarlet colour, and resembles, in this respect, the blood of vertebrated ani- 

 mals. 



VOL. II. 24 



