48 THE EARTH-WORM, CONSIDERED 



portion a perfect worm is never evolved, although it continues to live 

 for a month or two, and groAvs in some degree. If the division is 

 made into three parts, the middle and hinder ones die after some 

 weeks' struggle for existence and some efforts at reparation. The 

 mouth and lips are perfectly reproduced, provided the cerebral gan- 

 glions have not been included in the section. 



The natural uses of the worm appear to be to serve as nourishment 

 to moles, hedgehogs, frogs, toads, snakes, lizards, birds, fishes, and 

 some kinds of insects. It is also said by naturalists that worms are 

 useful to plants by penetrating the soil, loosening it, rendering it per- 

 meable to air and water, and even adding to the depth of the soil by 

 bringing up their worm-casts to the surface. Soil is not loosened by 

 boring through it, but rather rendered firmer in the parts not bored 

 through ; and so far from the surface soil being rendered permeable 

 by water in consequence of the bores of worms, it is rendered less so, 

 the worm-casts deposited on the orifices of the bores always being 

 water-tight ; so much so, indeed, that when lawns where worms abound 

 are to be watered by lime-water in order to destroy them, the first 

 step is to brush away the worm- casts with a long flexible rod, or 

 remove them by a rake or stubby broom, in order to let the water 

 enter the bores ; it having been found from experience, that, when 

 this operation is neglected, the lime-water sinks into the soil without 

 producing much effect. With impervious loamy sub-soils, resting on 

 gravel, the case is otherwise ; and under such circumstances worms 

 may be useful, by permitting the escape of water where it would 

 otherwise be retained. The surface orifices of some burrows may also 

 be left open, or perhaps partially closed ; but this is not the case, as 

 far as we are aware, except during those periods in the night, or in 

 dull moist weather, when the worms have partially left their holes. 

 With respect to worms adding to the depth of the soil (an opinion first 

 promulgated, we believe, by Mr. Darwin, before the Geological Society 

 in 1837, see page 505 of the Journal for that year, and still adhered 

 to by him), it is extremely doubtful whether it takes place to any 

 appreciable extent. According to this distinguished naturalist, how- 

 ever, the surface soil is raised by the agency of worms about the 

 seventh part of an inch annually. This theory may well be ques- 

 tioned, and we may perhaps better attribute the undoubted growth of 

 the thickness of siirface soil, as proved by top dressings that had 

 previously been applied to the surface, being found from six to 

 twelve inches below it, to the action of gravitation, the decompo- 

 sition of roots, and the deposit of an annual layer of carbon from 

 the atmosphere. 



The injury done by worms in gardens is much more apparent than 

 their soil-deepening powers. By their casts they disfigure walks and 

 lawns, and by cutting through the roots they injure more or less all 

 plants whatever, and particularly those which are weak (to which 

 worms always attach themselves more than to healthy plants), and 

 plants in pots. Seedlings of all kinds are much injured by them, be- 

 cause when the point of the taproot is cut through, the seedling has 



