268 



MANUAL OF ZOOLOGY. 



intestine, and the epithelium of the alimentary canal, like that 

 of the preceding orders, is ciliated. 



The pseudohaemal system is well developed, and consists 

 essentially of a long dorsal vessel, and a similar ventral one, 

 connected by transverse branches, and sometimes furnished at 

 the bases of the branchiae with pulsating dilatations. The 

 contained fluid is mostly red, but is yellow in Aphrodite and 

 Polynoe, and in no case contains corpuscles. 



Respiration is carried on by means of a series of external 

 branchiae or gills, arranged in tufts upon the sides of the body 

 on its dorsal aspect, along the middle of the body only, or 

 along its entire length ; but in some forms the gills may be 

 rudimentary or wanting. From the position of the branchiae, 

 the members of this order are often spoken of as the " Dorsi- 

 branchiate " (or more properly " Notobranchiate ") Annelides. 



Fig. 132. Cirrhatulus grandis. an "Errant Annelide." in its living condition. 

 (After Verrill.) 



The "segmental organs," with few exceptions, communicate 

 with the perivisceral cavity internally, and in certain segments 



