204 ELEMENTARY ZOOLOGY. 



appendages when present of simple bristles, not jointed 

 like the legs of the grasshopper ; the large, well-developed 

 body cavity; and the paired tubules of excretion. 



221. Classification of Segmented Worms. 



Setae present Class Chcetopoda. 



Setae few and simple Sub-class Oligochaeta. 



Small, chiefly aquatic Order Naidomorpha. 



Examples: Nais, Dero, Tubifex. 



Larger, living chiefly in the s:il. . .Order Lumbricomorpha. 

 Examples : Earthworms. 



(Lumbricus; Allolobophora; Diplocardia) . 

 Setae numerous, on a complex foot-like organ. 



Sub-class Polychaeta. 

 Free-swimming; head distinct; carnivorous. 



Order Errantia (wandering). 

 Example: Nereis, the sand-worm. 

 Tube-living ; head not distinct ; not actively carnivorous. 



Order Sedentaria (fixed) . 

 Examples: Amphitrite; Cirratulus; Serpula. 



Setae wanting; suckers present Class Discophora. 



Examples: 



Hirudo medicinalis, a parasite. 

 Aulostoma, free and carnivorous. 

 Hamidipsa, a land leech. 



222. Topics for Themes in Zoology or English. i. 

 Compare the " segments" in the segmented worms and 

 the tape- worm. 



2. What organs in the worm are derived from ectoderm? 

 from entoderm? from mesoderm? 



3. In the chaetopods what sets of organs pass through 

 all the segments? Which are repeated in nearly all? 

 Which are limited to a few? 



4. In what ways do earthworms benefit the soil ? Read 

 portions of Darwin's "Formation -of Vegetable Mould." 



5. Why is the anterior end of the digestive tract of the 

 earthworm more highly differentiated than the posterior 

 end? 



