310 



ORDER TERRICOL.E ; EARTH-WORM. 



worms, appears from the fact that, in the soil thus formed, large 

 numbers of " worm-casts " may be distinguished. These are 

 produced by the digestive process of the Worms ; which take 

 into their intestinal canal a large quantity of the soil through 

 which they burrow, extract from it the greater part of the 

 decaying vegetable matter it may contain, and reject the rest in 

 a finely-divided state. In this manner, a field, manured with 

 marl, has been covered, in the course of 80 years, with a bed of 

 earth averaging thirteen inches in thickness. 



845. It is commonly supposed that the Earth- Worm may 

 be multiplied by the division of its body 

 into two pieces, of which each will 

 continue to live. This does not, however, 

 appear to be the case with regard to the 

 common species. If it be divided across 

 the middle, when in motion, each part 

 will continue to move for a time ; but 

 only the piece which bears the head will 

 be found alive after a few hours. This 

 forms a new tail ; and soon shows little 

 sign of injury. But if the division be 

 made near the head, the body will re- 

 main alive, and will renew the head ; 

 and the head, with its few attached 

 segments, will die. There appear, how- 

 ever, to be some species, in which this 

 reproductive power is sufficiently great 

 to produce a new head and body from 

 even a small portion of the original ; 

 so that above twenty individuals have 

 been produced in this manner, by the 

 division of a single one into as many 

 parts. This power is even greater in the 

 Naids ; which also produce buds, that 

 separate from the parent by spontaneous 

 division, as in the Nereis prollfera 

 ( 836). The propagation of the Earth- 

 worms presents some other very remarkable peculiarities. The 



FIG. 531. LUMBRICUS TER- 

 RESTRIS, OR EARTH-WORM ; 6, 

 anterior segments magnified, 

 showing the bristles directed 

 backwards ; c, egg enclosing 

 two young ; ^.escape of young 

 worm from the egg. 



