ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 889 



Mr. Darwin shows that what is generally called " vegetable " 

 mould is almost solely the work of worms, and is, therefore, more 

 animal than vegetable. They are constantly swallowing earth and 

 small stones, and passing them through their bodies to the surface in 

 a finely triturated and fertilized condition ; so they may be said to 

 manure the earth inside their own bodies. By means of this process 

 the entire earthy surface of a country is constantly in a state of 

 change ; probably, all over, there are in every acre of land from 35,000 

 to 50,000 worms, and with so many at work, it is not difficult to 

 imagine what vnM be the effect of a constant accumulation of their 

 casts. In some cases, if spread over the ground, they would measure 

 one-fifth of an inch in depth per year, equal to one inch of earth 

 brought up from below, passed through the bodies of worms, and de- 

 posited on the sui'face in five years. In one instance 12 oz. of castings 

 were thrown up in a year on a square foot, or 6 • 75 lbs. on the square 

 yard, equal to 14^ tons of so-called fertile " vegetable " mould over an 

 acre in one year. Leaves and stones and lime and other substances 

 spread over a field, and left untouched, have been found in a very few 

 years several inches below the surface in a uniform layer. This, 

 there can be no doubt, from the data supplied by Mr. Darwin, is all 

 the work of worms. The millions of leaves and other vegetable 

 matter dragged by the creatures underneath the soil, whether passed 

 through theii' bodies or not, form a natural manure. Not only so, but 

 " the bones of dead animals, the harder jDarts of insects, the shells of 

 land molluscs, are before long all buried beneath the accumulated 

 castings of worms, and are thus brought in a more or less decayed 

 state within reach of the roots of plants." They are also a powerful 

 factor in geology, performing a great part in the disintegration of 

 rocks, not simply by direct action on the softer kinds, but by the in- 

 direct action of the acids which are mingled in their bodies with 

 whatever they swallow, and which will have a slow but ultimately 

 powerful efiect on even hard rocks. 



Mr. Darwin also shows that there is the greatest probability that 

 whole towns, like the old Roman towns of Silchester and Uriconium, 

 owe their preservation for the insjiection of modern archaeologists to 

 a large extent to the ceaseless work of generations of these creatures, 

 showdng the great effects of a continually recurring cause, even when 

 it seems almost infinitesimally small. 



As to the powers of special sense, Mr. Darwdn confirms the obser- 

 vations of Hofimeister that worms, although without eyes, are sensitive 

 to light. They are totally deaf to aerial vibrations, while very sensi- 

 tive to the vibration of any solid object with which they may be in 

 contact. Experiment also showed that the sense of smell is confined 

 to the perception of certain odours, viz. to those emitted by natural 

 food ; and the presence of taste was proved by the preference shown 

 for some kinds of cabbage over others. Of all their senses, however, 

 that of touch, including in the term the perception of vibration, seems 

 much the most highly developed. 



Experiments on the intelligence of the worms were made by 

 observing the mode in which they dragged leaves and triangles of 



