68 



Invertebrate 



elongated or sac-like bodies contain a long tortuous in- 

 testine, ciliated inside and outside. They rarely exhibit 

 a division into segments, nor have they locomotory pro- 

 cesses of any kind, and they never have any calcareous 



FIG. 40. 



FIG. 41. 



Tooth and Muscles 

 of Leech. 



Embryo Leech. Adult Leech. 

 Mouth of Leech. 



or siliceous spicules in their skin, although sometimes 

 there are a few bristles scattered on the surface. The 

 mouth is at the anterior end, and it is provided with 

 a protrusible proboscis, sometimes of great length. 



CLASS VII. Leeches. The next group of worms 

 is exemplified by the common horse-leech or by the 

 medicinal leech. They are soft-bodied annulated 

 worms which live parasitically on the outside of verte- 

 brated animals, from which they draw their nourish- 

 ment. Their bodies are composed of segments, which 

 are indistinctly or not at all marked from each other 



