Oct. 13, 1 881] 



NATURE 



555 



and we may infer — improbable as is the inference — that 

 worms are able by some means to judge which is the best 

 end by which to draw triangles of paper into their 

 burrows." 



On the question of defining such action as intelligent 

 or non-intelligent, Mr. Darwin refers to the criterion 

 " that we can safely infer intelligence only when we see 

 an individual profiting by its own individual experience"; 

 and he adds that "if worms are able to judge, either 

 before or after having drawn an object close to the 

 mouths of their burrows, how best to drag it in, they 

 must acquire some notion of its general shape," and 

 thus guide their actions by the result of individual 

 experience. 



Assuredly these observations are most interesting, and 

 it would seem well worth while to try whether, by a series 

 of lessons with similar triangles of paper, an individual 

 worm could be taught to lay hold of the apex in a greater 

 and greater proportional number of cases ; if so, there 

 could no longer be any question as to the intelligent 

 nature of the action. 



The only other observations with which we are ac- 

 quainted pointing to the existence of intelligence in 

 annelids are those of Sir E. Tennant ("Natural History 

 of Ceylon," p. 481). 



The remaining chapters of the book are occupied with 

 the subject of its title, and in their course many quanti- 

 tative results are given of the amount of mould which 

 worms are able to cast up. Thus, for instance, a certain 

 field was thickly covered with marl. Twenty-eight years 

 afterwards this layer of marl was found buried by mould 

 to a depth varying between twelve and fourteen inches. 

 Several other similar cases are given, the most interesting 

 being that of a field which adjoins Mr. Darwin's own 

 house. This was last ploughed in 1841, then harrowed, 

 and left to become pasture land. Then 



" For several years it was clothed with an extremely 

 scant vegetation, and was so thickly covered with small 

 and large flints (some of them half as large as a child's 

 head) that the field was always called by my sons ' the 

 stony field.' When they ran down the slope the stones 

 clattered together. I remember doubting whether I should 

 live to see these larger flints covered with vegetable mould 

 and turf. But the smaller stones disappeared before many 

 years had elapsed, as did every one of the larger ones 

 after a time; so that after thirty years (1871) a horse 

 could gallop over the compact turf from one end of the 

 field to the other, and not strike a single stone with his 

 shoes. To any one who remembered the appearance of 

 the field in 1842, the transformation was wonderful. This 

 was certainly the work of the worms, for though castings 

 were not frequent for several years, yet some were thrown 

 up month after month, and these gradually increased in 

 numbers as the pasture improved. In the year 1871 a 

 trench was dug on the above slope, and the blades of 

 grass were cut off close to the roots, so that the thickness 

 of the turf and of the vegetable mould could be measured 

 accurately. . . . The average accumulation of the mould 

 during the whole thirty years was only 083 inch per year; 

 but the rate must have been much slower at first, and 

 afterwards considerably quicker." 



Numberless other corroborative cases are given, but we 

 have no further space to enter into their details. Large 

 stones are slowly undermined and sunk by worms, and 

 woodcuts are given to illustrate actual measurements 

 made by Mr. Darwin or his sons of the rate of sinking 



in particular cases. These measurements show that in 

 the cpurse of two or three centuries large blocks of stone 

 (e.g. 67 X 39 X 15 inches) may become completely buried. 

 Thus we are not surprised to learn that old pavements 

 and low walls are subject to the same process, and many 

 instances are given which have been observed by Mr. 

 Darwin or his sons of the remains of Roman houses 

 buried so far beneath the soil that the latter has been 

 ploughed for years without any one having suspected the 

 presence of walls and pavements beneath. In some cases 

 the thickness of the mould or soil above such remains 

 was found to be twenty, thirty, and even forty inches. 



The actual weight of worm-castings thrown up in one 

 year was calculated in one case to amount to i8'l2 tons 

 per acre. 



Such being the work that worms are able by their 

 gradual and cumulative action to accomplish, it becomes 

 evident, as pointed out in Mr. Darwin's paper more than 

 forty years ago, that worms must play an important part 

 in the process of denudation. This topic is therefore 

 treated at length, and it is shown that over and above the 

 mechanical action already described, worms materially 

 assist the process of denudation by the chemical actions 

 incidental to digestion. For 



" The combination of any acid with a base is much 

 facilitated by agitation, as fresh surfaces are thus con- 

 tinually brought into contact. This will be thoroughly 

 effected with the particles of stone and earth in the 

 intestines of worms, during the digestive process ; and it 

 should be remembered that the entire mass of the mould 

 over every field, passes, in the course of a few years, 

 through their alimentary canals. Moreover as the old 

 burrows slowly collapse, and as fresh castings are con- 

 tinually brought to the surface, the whole superficial layer 

 of mould slowly revolves or circulates ; and the friction 

 of the particles one with another will rub off the finest 

 films of disintegrated matter as soon as they are formed. 

 Through these several means minute fragments of rocks 

 of many kinds and mere particles in the soil will be con- 

 tinually exposed to chemical decomposition ; and thus 

 the amount of soil will tend to increase.'' 



And, 



" The several humus-acids, which appear, as we have 

 just seen, to be generated within the bodies of worms 

 during the digestive process, and their acid salts, play a 

 highly important part, according to the recent observa- 

 tions of Mr. Julien, in the disintegration of various kinds 

 of rocks." 



Further, 



" The trituration of small particles of stone in the 

 gizzards of worms is of more importance under a geologi- 

 cal point of view than may at first appear to be the case ; 

 for Mr. Sorby has clearly shown that the ordinary means 

 of disintegration, namely, running water and the waves 

 of the sea, act with less and less power on fragments of 

 rock the smaller they are." 



This assistance which worms lend to the process of 

 denudation is of special importance in the case of flat or 

 gently-inclined surfaces, for here it is not improbably the 

 chief agent at work. Castings thrown up during or 

 shortly before rain flow for a short distance down an in- 

 clined surface, and the finest earth is washed completely 

 away. Again, during dry weather, the disintegrated 

 castings roll as little pellets, and a strong wind blows all 

 the castings, even on a level field, to leeward. 



One other observation must be quoted, which, besides 



