554 



NATURE 



{Oct. 13, 1881 



any solid object with which they may be in contact, as 

 was shown, among other ways, by placing flower-pots 

 containing worms in their burrows upon a piano ; on 

 striking single notes, whether high or low, the worms 

 instantly I'etreated. In this connection, also, the fol- 

 lowing may be quoted : — 



" It has often been said that if the ground is beaten or 

 otherwise made to tremble, worms believe that they are 

 pursued by a mole, and leave their burrows. I beat the 

 ground in many places where worms abounded, but not 

 one emerged. When, however, the ground is dug with a 

 fork and is violently disturbed beneath a worm, it will 

 often crawl quickly out of its burrow." 



Regarding smell, the interesting result was obtained, 

 that the sense is "confined to the perception of certain 

 odours " — namely, those emitted by natural food. For 

 while the animals showed themselves indifferent to 

 tobacco juice, paraffin, c&c, held near them, pieces of 

 cabbage-leaf, onions, &c., when buried near an earth- 

 worm, were always discovered by the animal. 



The presence of taste was proved by the fact that the 

 worm showed a preference for some varieties of cabbage 

 over others ; but " of all their senses, that of touch, in- 

 cluding in the term the perception of vibration, seems 

 much the most highly developed." 



Worms are omnivorous, dragging pieces of meat as 

 well as leaves into their burrows for the purpose of eating 

 them. They smear the leaves so drawn in with a secreted 

 fluid. This fluid is alkaline, and acts both on the starch 

 granules and on the protoplasmic contents of the cells ; 

 it thus resembles in nature the pancreatic secretion, and 

 serves partly to digest the leaves before they are taken 

 into the alimentary canal — so constituting the only case 

 of extra-stomachal digestion hitherto recorded in an 

 animal — its nearest analogy being perhaps that of the 

 digestive fluid of Drosera or Dionoea, " for here animal 

 matter is digested and converted into peptone not within 

 a stomach, but on the surface of the leaves." 



We now come to one of the most interesting chapters, 

 which deals with the habit of dragging down leaves, &c., 

 into the burrows ; for here the e.xperiments elicited some 

 very remarkable evidence of action which is apparently 

 intelligent. These e.xperiments are thus led up to. 



'•' Worms seize leaves and other objects, not only to 

 serve as food, but for plugging up the mouths of their 

 burrows ; and this is one of their strongest instincts. 

 Leaves and petioles of many kinds, some flower-peduncles, 

 often decayed twigs of trees, bits of paper, feathers, tufts 

 of wool and horse-hairs are dragged into their burrows 

 for this purpose. . . . When worms cannot obtain leaves, 

 petioles, sticks, &c., with which to plug up the mouths of 

 their burrows, they often protect them by little heaps of 

 stones ; and such heaps of smooth rounded pebbles may 

 frequently be seen on gravel-walks. Here there can be 

 no question about food. A lady, who was interested in 

 the habits of worms, removed the Httle heaps of stones 

 from the mouths of several burrows and cleared the 

 surface of the ground for some inches all round. She 

 went out on the following night with a lantern, and saw 

 the worms wiih their tails fixed in their burrows, dragging 

 the stones inwards by the aid of their mouths, no doubt 

 by suction. ' After two nights some of the holes had eight 

 or nine small stones over ihem ; after four nights one had 

 about thirty, and another thirty-four stones.' One stone 

 which had been dragged over the gravel-walk to the 

 mouth of a burrow weighed two ounces ; and this proves 

 how strong worms are." 



The object of this plugging Mr. Darwin surmises to be 

 that of " checking the free ingress of the lowest stratum 

 of air when chilled by radiation at night." 



Now, concerning the apparent intelligence displayed in 

 these plugging operations, Mr. Darwin " observed care- 

 fully how worms dragged leaves into their burrows ; 

 whether by their tips or bases or middle parts. It seemed 

 more especially desirable to do this in the case of plants 

 not natives to our country ; for although the habit of 

 dragging leaves into their burrows is undoubtedly in- 

 stinctive with worms, yet instinct could not tell them how 

 to act in the case of leaves about which their progenitors 

 knew nothing. If, moreover, worms acted solely through 

 instinct or an unvarying inherited impulse, they would 

 draw all kinds of leaves into their burrows in the same 

 manner. If they have no such definite instinct, we might 

 expect that chance would determine whether the tip, base, 

 or m.iddle was seized. If both these alternatives are ex- 

 cluded, intelligence alone is left ; unless the worm in 

 each case first tries many different methods, and follows 

 that alone which proves possible or the most easy ; but 

 to act in this manner and to try different methods makes 

 a near approach to intelligence." 



A large number of experiments were therefore tried 

 with leaves of various shapes, and both of endemic and 

 exotic species. The results showed unequivocally that 

 the part of the leaf which the worm seized for the purpose 

 of dragging the whole into the burrow was not a matter 

 of chance, but in an overwhelming majority of cases that 

 part of a leaf was seized by the dragging of which the 

 leaf would offer least resistance to being drawn into the 

 burrow. Thus, for instance, " the basal margin of the 

 blade in many kinds of leaves forms a large angle with 

 the foot-stalk ; and if such a leaf were drawn in by the 

 foot-stalk, the basal margin would come abruptly into 

 contact with the ground on each side of the burrow, and 

 would render the drawing in of the leaf very difficult 

 Nevertheless worms break through their habit of avoiding 

 the foot-stalk, if this part oflers them the most convenient 

 means for drawing leaves into their burrows." 



Again, in the case of pine-leaves consisting of two 

 needles joined to a common base, it is almost invariably 

 by this base that the worm draws in the pair of leaves, 

 and it is evident that, as the worm cannot lay hold of the 

 two diverging points at the same time, this is the only 

 part of the leaf by seizing which they would be able to 

 drag the whole into their burrows. Mr. Darwin tried in 

 some leaves tying or cementing the two diverging points 

 together ; but the worms still preferred the bases. Still 

 further to test the hypothesis of chance, elongated tri- 

 angles were cut out of paper and given to the worms 

 instead of leaves. Here " it might certainly have been 

 expected, supposing that worms seized hold of the tri- 

 angles by chance, that a considerably larger proportion 

 would have been dragged in by the basal than by the 

 apical part " ; while, inasmuch as the latter was in a literal 

 sense the thin end of the wedge, it was the part which 

 intelligent action would be most likely to choose. The 

 results of many experiments with these paper triangles 

 showed that " nearly three times as many were drawn in 



by the apex as by the base We may therefore 



conclude that the manner in which the triangles are 

 drawn into the burrows is not a matter of chance, .... 



