46 PRACTICAL ZOOLOGY. 



in appearance. In classifying animals, the more significant 

 characters are internal structure and mode of development 

 rather than mere outer form and general appearance. Most 

 worms have gills. Worms never have jointed appendages. 



There is a group of slender worms called hair-worms. 

 " They sometimes occur in horse-troughs, whence they are 

 supposed by the ignorant to be transformed horse-hairs." 



In what characters are worms like Arthropods ? How 

 do worms differ from Arthropods ? 



Read the life history of the tapeworm and the trichina. 



Read Darwin's " Vegetable Mould and Earthworms," 

 the description of the earthworm in Huxley's "Anatomy 

 of Invertebrated Animals," "Anatomy of the Earthworm" 

 in Brooks' " Handbook of Invertebrate Zoology," " Worms 

 and Crustacea," No. VII in Hyatt's " Guides for Science 

 Teaching." 



THE FRESH-WATER CLAM. 



STUDY OP THE LIVE CLAM. 



Look for fresh-water clams in the sandy bottoms of creeks 

 and rivers. They may be found nearly buried in the sand or 

 mud. If no better aquarium be at hand, take an old tub, 

 half fill it with water, and have two or three inches of 

 sand at the bottom. Drop several clams into the water, 

 and note carefully the place and position of each. On the 

 next day see if any of them have changed either place or 

 position. The part uppermost, in the natural position, is 

 the back. Look near one end, where the shell opens a 

 little, for two oval holes. These are the siphons; gently 



