64 ANNELIDANS. 



furnished with black spots, which appear to be eyes of very simple 

 structure. They often have on the head, or on 

 the sides of the neck, fleshy filaments called 

 tentacles, which are not only delicate instru- 

 ments of touch, but sometimes perform other 

 important functions, as we shall see hereafter. 

 In general, these animals can crawl upon the 

 ground by means of their setae ; many live 

 buried in the earth, or are enclosed in tubes 

 which they never leave. They mostly inhabit 

 the sea, and are, with one or two exceptions, 

 FIG. 58. FOOT OF NAIS. carnivorous. 



The Annelidans are divided by zoologists 



into three Orders, according to the nature and disposition of their 

 respiratory apparatus. Some appear to breathe by the general 

 surface of their bodies, and have no special respiratory organs 

 visible externally; these, therefore, have been called Abranchia,* 

 without gills. 



In a second division the breathing apparatus consists of a series 

 of tufts (Fig. 63) or fringes, arranged along the middle or on each 

 side of the back ; these are the Dorsibranchiata.f 



In the third Order, Tubicola, J the Annelids inhabit a tube, 

 either-composed of shell or manufactured by the agglutination of 

 various materials. These have their branchiae in the form of 

 plumes or branching filaments attached to the head or neck 

 (Fig. 65). 



FIRST ORDER ABRANCHIATE ANIMALS. 



This Order comprehends two families, which differ widely from 

 each other. The Setig"era, which have locomotive appendages 

 in the shape of delicate spines or bristles (Earthworm, Nais) ; 

 and Suctoria, || which are destitute of such appendages, but are 

 furnished instead with a prehensile sucker attached to each ex- 

 tremity of the body (Leeches). 



The Earth,- Worms (Lnmbricus). The common well-known species (Lumbricus 

 terrestris] attains nearly a foot in length ; its body is composed of 120 rings or more, and 

 is completely destitute of eyes or tentacles. Though a humble and despised creature, 

 the earth-worm is a most important item in the economy of Nature. Piercing the 

 ground in every direction, the earth is lightened by the united labours of their countless 

 legions, and thus they materially conduce to its fertility. It consumes upon the surface 



* A, not, and branchia, a gill. t Dorsum, the back ; branchia, a gill. 



\ Tubus, a tube ; colo, / inhabit. Seta, a bristle ; gero, I carry. 



|| Suctorius, sucking. 



