Lumbricus extends from the thirty-second to the 

 thirty-seventh segment as counted from the anterior 

 end. In Eisenia the ghmduhir enlargement lies in seg- 

 ments twenty-five through thirty-two. The cocoons 

 produced are similar, about the size of a grain of 

 wheat in Lumbricus, slightly smaller in Eisenia. 

 Those of the giant 1 1-foot earthworm MegascoUdes 

 australis of Australia are almost three inches long 

 and half an inch in diameter — about two-thirds as 

 thick as the slender worm itself. 



Some kinds of South Asian earthworms appear 

 able to regenerate new individuals from both parts 

 if they are cut in two. Earthworms in the northern 

 parts of Europe and Asia, Australia, Africa, and the 

 Western Hemisphere cannot do this. They will re- 

 place four or five segments at the anterior end, and 

 this may be the most they will do even if the loss 

 there is as great as ten segments. On the other hand, 

 a cut between segments eleven and thirty-six is al- 

 most sure to kill the worm. 



If its first thirty-five segments remain intact, a well- 

 nourished worm may regenerate a new posterior 

 end and add segments closely matching the number 

 amputated. Somehow the worm is able to install re- 

 placements bringing the total almost exactly to the 

 tally at hatching age. 



In most soils, earthworms constitute about half of 

 the entire weight of animal life. Half a ton of earth- 

 worms to the acre is an average figure. In rich soil 

 it may reach twelve tons to the acre, which could be 

 regarded as a fair indicator of fertility. Appreciation 

 of the earthworm's role in the soil is far younger than 

 a knowledge of its use in angling. Juliana Berners, a 

 nun in an English Benedictine convent, gave clear in- 

 structions for finding and using worms as bait in the 

 fifteenth century. Aristotle referred to earthworms 

 inelegantly as "earth's guts," but he recorded no 

 knowledge of where they came from or any value 

 they might have. 



Not until 1777 was the value of earthworms to 

 plant economy guessed at by the English naturalist 

 Gilbert White, who wrote: 



Earthworms, though in appearance a small and des- 

 picable link in the chain of nature, yet. if lost, would 

 make a lamentable chasm. For to say nothing of half 

 the birds, and some quadrupeds which are almost 

 entirely supported by them, worms appear to be great 

 promoters of vegetation . . . the earth without them 

 would soon become cold, hard-bound, and void of 

 fermentation, and consequently sterile. 



Less than a century ago, Charles Darwin published 

 a fuller account. The Foifiuition of Vegetable Mould 

 through the Action of Worms, a book drawing to- 

 gether extensive observations which showed how 

 much of the humus matter in the soil came from 

 leaves and other plant debris pulled by earthworms 

 into their subterranean tunnels. The passageways 



also serve vegetation by admitting oxygen and rain. 

 Darwin summarized his discoveries with the state- 

 ment: 



The whole of the superficial mould [topsoil] over any 

 such expanse has passed, and will again pass, every 

 few years through the bodies of worms. The plough 

 is one of the most ancient and most valuable of man's 

 inventions; but long before it existed the land was in 

 fact regularly ploughed and still continues to be thus 

 ploughed by earthworms. 



Darwin collected the castings over sample areas of 

 ground, and dried and weighed the material col- 

 lected. He estimated that between seven and one-half 

 and eighteen tons of material were annually brought 

 to the surface by worms in each acre of ground. 

 Later scientists found that the amount of earth-mov- 

 ing actually ranges from two or three tons per acre per 

 year in light soils to more than a hundred tons in 

 some tropical parts of the world. 



The conspicuous saddle-shaped clitellum of earth- 

 worms secretes the cylindrical sheath which becomes 

 the "cocoon" for developing eggs. ( Bavaria. Otto Croy ) 



