ANNELIDS. 63 



curious confirmation, in a paper communicated by Mr. Darwin* 

 to the Geological Society of London, in Nov. 1837. He ob- 

 serves that, in a pasture field which has long remained 

 undisturbed, not a pebble will be seen, although, in an adjoining 

 ploughed field, a large proportion of the soil may be composed 

 of loose stones. This he attributes to the working of worms, 

 and states his conviction, that every particle of earth in old 

 pasture land has passed through the intestines of worms; and 

 hence that, in some senses, the term " animal mould" would 

 be more appropriate than " vegetable mould." It has been 

 estimated that, in eighty years, the marl laid upon a field for 

 manure, has been covered with soil to the depth of thirteen 

 inches, by the operations of these creatures. 



44 It is commonly supposed," says Dr. Carpenter, " that 

 the earth- worm may be multiplied by the division of its body 

 into two pieces, of which each will continue to live. This, 

 however, does not 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 remain alive, and will renew the head; and the head, 

 with its few attached segments, will die."t 



The power of reproduction is enjoyed by many other 

 Annelids to a much greater extent. A small worm (Lumbricus 

 variegatus) was cut by Bonnet, a French naturalist, into 

 twenty-six parts, and " almost all of them reproduced the 

 head and tail, and became so many new and perfect indivi- 

 duals. It sometimes happened, that both ends of a segment 

 reproduced a tail. Wishing to ascertain if the vegetative 

 power was inexhaustible, Bonnet cut off the head of one of 

 these worms, and, as soon as the new head was completed, he 

 repeated the act ; after the eighth decapitation, the unhappy 

 subject was released by death." { 



In some species, the propagation reminds us of that of 

 which we saw examples in the Infusoria. Thus, "in the Nais, 



* Vide, [Note to White's Selborne, edited by Rev. L. Jenyns, 184.3, and 

 Penny Cyclopedia, Lumbricus. 

 f Zoology, vol. ii. page 310. 

 j Owen, page 143. 

 Carpenter's Physiology, page 549. 

 PART i. D 2 



