THE EARTHWORM. 45 



do many different things. A part of an animal having a 

 special work to do is called an organ, and its work is its 

 function. The earthworm has many organs, but few 

 functions. Apply this principle to man and an ape. Each 

 has four limbs. The ape is called four-handed, but has no 

 good hands; he cannot handle things well. He has not 

 good feet ; he cannot walk well. What is the one thing he 

 can do well with his four foot-hands ? How many distinct 

 functions has man with his hands and feet ? Multiplica- 

 tion of parts without corresponding variety of structure 

 and function mark an animal as low in rank. 



Another respect in which the earthworm is low is this, — 

 the head end is not much better than the tail end. There 

 is no distinct head. At first glance there is not much 

 difference. Many worms similar to the earthworm may be 

 cut in two, and each part lives ; the hind part developing a 

 new head, and the fore part a new tail. The part of the 

 nervous system in the head is not greatly different from 

 other parts. Just in proportion as the head rises in 

 importance, and the whole set of organs centre around it, 

 the animal rises in the scale. Apply this test to the earth- 

 worm and crayfish, crayfish and crab, bee and dragon-fly. 



Compare insects with earthworms in rank from another 

 point of view. Most insects, before reaching the adult 

 state, pass through a worm-like stage. Crabs are at first 

 like crayfishes in having a Avell developed abdomen. As the 

 crab grows, the abdomen shortens, and the head becomes 

 more prominent. What would this indicate as to the 

 relative rank of worms and insects? of crayfishes and 

 crabs? Worms constitute one branch of the animal 

 kingdom. In this branch, Vermes, are the leech, trichina, 

 tapeworm, with many animals very unlike the earthworm 



