ORDERS OF ANNELIDANS. 85 



t vd br br br br vd 



\ \ 



tr \ 



av vi va 



Fig. 74. ANATOMY OF ANNELIDANS. 



8. According to the differences in their respiratory organs, this 

 class is divided into three orders; namely, 



1st. The abranchiate anne'lidans (from the Greek, a, without, 

 and bragchos, branchia, or gills), in which there is no visible 

 respiratory apparatus. 



2d. The dorsibranchiate anne'lidans (from the Latin, dorsum, 

 back, and branchia, gills), in which the branchiae are arranged 

 along the middle or on each side of the back, in form of vascular 

 tufts, fringes, &c. (fig. 74, br). 



3d. The tubicola tubicole anne'lidans (from the Latin, tubus, 

 a tube, and colo, I inhabit) inhabit a fixed and permanent resi- 

 dence, which encloses and defends them. The two preceding 

 orders are erratic. The branchiae are in form of plumes or 

 branches attached to the anterior part of the body (fig. 80). 



9. The abrarichia this order comprehends two very distinct 

 families : the terricola setigerous abran'chiate anne'lidans, which 

 have the body furnished with seta3 (bristles), serving them for 

 locomotion, and the sucto'ria or suctorial abran'chiate anne'lidans, 

 which are without setce, but have a prehensile sucker attached to 

 each extremity of the body. 



10. To the family of terrico'la (from the Latin, terra, earth, 

 and colo, I inhabit) belongs the lumbricus or earth-worm, so com- 

 mon in our gardens. The body of these animals is cylindrical, 

 elongated, and divided by plaits into a great many rings, and 

 they are totally destitute of legs ; in place of them, we find on 



Explanation of Fig. 74. Anatomy of anne'lidans longitudinal section 

 of an Arenicola ; t, the cephalic extremity ; 6, the mouth ; tr, the trunk 

 or sucker ; ph, the pharynx ; e, the stomach ; i, the intestine ; a, the 

 anus ; br, the branchiae; c, one of the ventricles serving as a heart; ctJ, 

 ventral vessel ; ca, vessels which carry the blood to the branchiae ; ve, 

 vessels which bring- the blood back from the branchiaB to the interior ; vd, 

 dorsal vessel into which many of these last vessels empty ; ui, inferior in- 

 testinal vessel, which also receives vessels coming from the branchiae it 

 opens in the dorsal vessel near the heart. 



8. How is the class of anne'lidans divided ? 



9. How are anne'lidans of the order abran'chia characterized ? 

 10. What are the characters of the earth-worm ? 



8 



