218 



THE SCIENCE OF LIFE. 



of organization can easily be seen. The male rotifers 

 are few and small, and have no digestive canal, but the 

 females have a complete nutritive system, 

 and many species are provided with an organ 

 for mastication resembling an anvil acted on 

 by two hammers, another instance of pecul- 

 iarity of structure for a special end. These 

 animals are capable of reviving on being 

 moistened, after having been dried up, and 

 that many times in succession. (Fig. 120.) 



Order 8. Gcpliyrca, (gephura, a bridge,) so 

 called in allusion to the apparent connection 

 which they exhibit between Echinoderms and 

 Articulates. They are sometimes called 

 Spoon -worms, Squirt -worms, and Siphon- 

 worms, (Sipunculus.) They have all the as- 

 pect of worms, but the circle of tentacles 

 FIG. i2o.-Ro- round the mouth show their affinity to Ho- 

 lothurians. They live in the sand, or seek 

 protection in some empty univalve shell. Their elon- 

 gated bodies contain a long, tortuous intestine, ciliated 

 inside and outside. They have no locomotive processes, 

 nor are there calcareous or silicious spicules in their skin. 

 The mouth has a long proboscis. 



Order 9. Suctoria, or Leeches. These are aquatic 

 worms, with a soft, segmented body, provided with a 

 suctorial disk at one or both ends. The mouth of the 

 common Leech (Hirudo medicinalis) is armed with three 

 horny, semi-lunar plates, with finely serrated teeth, which 

 act as saws, enabling the leech to make incisions in the 

 skin of its host through which to suck the blood. 



