196 ELEMENTARY ZOOLOGY. 



organs of digestion, circulation, the nervous system and 

 sense organs, excretory system, and the like, are better 

 differentiated than in the phyla that have been studied. 



4. There is a well-developed body-cavity in which the 

 internal organs lie. 



214. The Earthworm. Practical Exercises for Field and Li- 

 brary. Habits. Where are earthworms to be found? In what 

 kinds of soil? How do the worms get through the soil? What 

 becomes of the dirt that was originally in the burrows? Make a 

 life-box not more than one-half inch in width, with glass sides, and 

 fill with moist earth. Put in this a number of worms and the under- 

 ground activities can be watched. How do they behave as the soil 

 dries at the top? Moisten it from the top. 



Locomotion. How do the earthworms move? Place one on a 

 moist surface and watch carefully every motion, so as to determine 

 just how the crawling is done. Set down, in order, the steps. Would 

 you say that there are any special organs of locomotion? Can he 

 move with either end foremost? What determines which will go 

 forward? Study, in the figures of your text-books, a cross-section 

 of the body of the animal. How are the muscles arranged? Will 

 this help you understand the actions? Identify the setas. Where 

 are they found ? 



General Form and Structure. Make a list mentioning all the 

 facts of external differentiation you can discover? Would you 

 say that the worm is simple or complex, externally ? Compare with 

 the grasshopper in this respect. Is it symmetrical? What paired 

 organs can you find? What differences in structure and behavior 

 between the anterior and the posterior ends? Between the dorsal 

 and ventral surfaces? 



Is the number of segments the same in the different specimens? 

 Are the segments all alike? How many depart in some way from 

 the general average? Where are these? Have these different seg- 

 ments any special meaning? Can you distinguish special regions 

 in the body, as you did in the crayfish or grasshopper? Locate the 

 mouth, the anal opening, the girdle (clitellum) . 



Make such drawings as are necessary to show the general external 

 structure. 



What color is the animal? What produces the color? Are all 

 equally transparent? Can you see any organs at all through the 

 body wall? 



Sensitiveness and the Nervous Organs. Devise experiments to test 



