NATURE 



553 



THURSDAY, OCTOBER 13, iS 



MR. DARWIN ON THE WORK OF WORMS 

 The Formation of Vegetable Mould through the Action of 

 Worms, with Observations on their Habits. By Charles 

 Darwin, LL.D., F.R.S. (London: John Murray, 1881.) 



IF the world were not already accustomed to the un- 

 precedented fertility of Mr. Darwin's genius, it might 

 well be disposed to marvel at the appearance of yet 

 another work, now added to the magnificent array of 

 those which bear his name. But feelings of wonder at 

 Mr. Darwin's activity have long ago been sated, and most 

 of us have grown to regard his powers of research as be- 

 longing to a class siti generis, to which the ordinary 

 measures of working capacity do not apply. Be our 

 feelings of wonder, however, what they may, it is most 

 gratifying to find that this latest work from the hand of 

 our illustrious countryman is in every way worthy of its 

 predecessors. Everywhere throughout the book we meet 

 with the distinctive attributes of Mr. Darwin's mind. 

 Beginning with matters of the most common knowledge, 

 which at first sight appear to furnish the most unpromis- 

 ing material, he proceeds by close observation of details 

 and sagacious manipulation of facts to establish general 

 truths of the most far-reaching importance in directions 

 where we should least have expected any such truths 

 to lie. 



But to avoid the presumption of seeming to commend 

 the work of so great a master, we shall proceed at once to 

 render an epitome of the work itself. This, as its title is 

 sufficient to denote, is an extension of the celebrated 

 paper " On the Formation of Mould," read before the 

 Geological Society in 1837 (See Trans. Geol. Soc. vol. v. 

 p. 505) ; but the extension is so considerable that the 

 present volume is really a new work. The subject, of 

 course, is the same ; but the later observations, Avhile 

 tending to confirm, and in fact to demonstrate, the 

 conclusions based upon the former, have served to swell 

 a short paper into a book of over 300 pages. Alluding to 

 this paper, Mr. Darwin writes : 



" It was there shown that small fragments of burnt marl, 

 cinders, &c., which had been thickly strewed over the 

 surface of several meadows, were found after a few years 

 lying at a depth of some inches beneath the turf, but still 

 forming a layer. This apparent sinking of superficial 

 bodies is due, as was first suggested to me by Mr. 

 Wedgwood, of Maer Hall, in Staffordshire, to the large 

 quantity of fine earth continually brought up to the 

 surface by worms in the form of castings. These castings 

 are sooner or later spread out, and cover up any object 

 left on the surface. I was thus led to conclude that all 

 the vegetable mould over the whole country has passed 

 many times through the intestinal canal of worms 

 Hence the term ' animal mould ' would be more appro- 

 priate than that commonly used of 'vegetable mould.'" 



Dealing ne.\t with criticisms which from time to time 

 have been made upon his original paper, Mr. Darwin 

 quotes one from Mr. Fisb, which we may here re-quote 

 on account of its instructive character. " Considering 

 their weakness and their size, the work they are repre- 

 sented to have accomplished is stupendous." On which 

 Mr. Darwin observes :— " Here we have an instance of that 

 inability to sum up the effects of a continually recurring 

 Vol. xxiv. — No. 624 



cause, which has often retarded the progress of science, 

 as formerly in the case of geology, and more recently in 

 that of the principle of evolution." He then adds ; — 



" Although these several objections seemed to me to 

 have no weight, yet I resolved to make more observations 

 of the same l;ind as those published, and to attack the 

 problem on another side ; namely, to weigh all the castings 

 thrown up w ithin a given time in a measured space, in- 

 stead of ascertaining the rate at which objects left on the 

 surface were buried by worms. But some of my obser- 

 vations have been rendered almost fuperfluous by an 

 admirable piper by Von Hensen, already alluded to, 

 which a]ipeared in 1S77. Before entering on details with 

 respect to the castings, it will be advisable to give some 

 account of the habits of worms fron my own observa- 

 tions and from those of other naturalists." 



Of these habits the most interesting are as follows : — 

 Although earth-worms are properly speaking terrestrial 

 animals, they are still " like the other members of the great 

 class of annelids to which they belong," semi-aquatic. For 

 while dry air is quickly fatal to them, they may live when 

 completely submerged in water for nearly four months. 

 Normally they live in burrows, and generally lie motionless 

 just at the mouth of the latter, so that by looking down 

 into the burrows the heads of the worms can be seen. 

 This habit of lying near the surface leads to their destruc- 

 tion in enormous numbers by birds. For, 



" Every morning during certain seasons of the year, 

 the thrushes and blackbirds on all the lawns throughout 

 the country draw out of their holes an astonishing number 

 of wor.iis ; and this they could not do unless they lay 

 close to the surface. It is not probable that worms 

 behave in this manner for the sake of breathing fresh air, 

 for we have'seen that they can live for a long time under 

 water. 1 believe that they lie near the surface for the 

 sake of warmth, especially in the morning ; and we shall 

 hereafter find that they often coat the mouths of their 

 burrows with leaves, apparently to prevent their bodies 

 fiom coming into close contact with the cold damp earth. 

 It is said that they completely close their burrows during 

 the winter." 



As regards powers of special sense, it has been observed 

 by Hoffmeister that, although destitute of eyes, earth- 

 warms are sensitive to light, time however being required 

 for the summation of the stimulus before it is responded 

 to. It is only the anterior extremity of the body, where 

 the cerebral ganglia are situated, that is thus sensitive to 

 light. These observations have been confirmed by Mr. 

 Darwin. He further found that the colour of the light 

 apparently made no difference in the result, nor did partly 

 filtering out the heat-rays by means of a sheet of glass ; 

 while a dull-red heated poker, held at such a distance from 

 the worms as would cause a sensible degree of warmth to 

 the hand, did not disturb them nearly so much as the light 

 from a candle concentrated by a lens. The sensitiveness 

 to light is less when a worm is engaged in eating or in 

 dragging leaves into its burrow — a fact which Mr. Darwin 

 is disposed to consider analogous to what in higher ani- 

 mals we know as the distracting influence of attention. 

 When not engaged in any active operation, the sensitive- 

 ness of worms to light is so considerable that " when a 

 worm is suddenly illuminated it dashes like a rabbit into 

 its burrow." 



With respect to hearing, all the experiments went to 

 show that worms are totally deaf to all kinds of aerial 

 vibration, although extremely sensitive to the vibration of 



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