KEW : ON THE MUCUH-TilKEADS OF LAND-SLUGS. 165 



exposed situations, near the glass, to which they had crawled during 

 the night. That observed by Eimer (30) was descending in the early 

 morning sun from a tree, and it occurred to the observer that the crea- 

 ture, surprised by the sun, had adopted this means of withdrawing 

 from the unpleasant influence. Slugs placed on grass-stems exposed 

 to the sun, Eimer fm-ther says, if they could not otherwise escape into 

 shade, invariably descended. Ward's slug (36) commenced to spin 

 " on being turned to the light"; and horror of exposure is shown, more- 

 over, by the creatures' behaviour, as above noted, when placed on 

 twigs ; their desire to escape is generally evident under all conditions 

 of light and shade, but their anxiety is increased, as I have noticed, 

 when they are exposed to the sun or even to the full light of a window. 

 Escape by this means from uncongenial dryness is illustrated by D.T. 

 (33) ^^'lio saw slugs descending by long threads from clover in a loft; 

 and still more interesting are the observations of Blandford {46) by 

 whom slugs were seen descending from corn-stacks at harvest-time. 

 AVhen the stubble is grassy many slugs collect m the butt-end of the 

 sheaves ; this end is placed outwards on the wagon or stack, and soon 

 gets dry, whereupon, Blandford tells us, tlie slugs find the surround- 

 ings uncongenial, and at once descend. Escape by the same means 

 from unpleasant environment of other kinds has also been observed : 

 a gardener (49) placing pieces of tobacco about a slug, saw it go to 

 and fro a few times, and then let itself down ; and, further, we have 

 the cases recorded by Eimer (30) in which slugs, dusted with lime, 

 quickly crept from leaves, and lowered themselves to the earth. 



All things considered, however, I cannot think that the animals 

 profit much by their spinning powers. There is no reason to suppose 

 tliat they would often come to grief if they dropped without a thread ; 

 which indeed they often do, sometimes by reason of the imperfection 

 of their thread-making, and sometimes without giving themselves a 

 chance of exercising it. Mr. S. C. CockerclF noted that Z. arboruin 

 on beeches, at Veules, clung very loosely and fell to the ground when 

 touched. Ariolimax cohnnbiajius, as we have seen, frequently falls 

 from trees; and from trials made by the writer a fall of a few feet does 

 not appear to injure the animals. It seems doubtful, finally, whether 

 the slugs' spinning faculty, such as it is, can be explained on the 

 ground of its utility, and I am inclined to regard the imperfect kind of 

 thread-making here obtaining as little more than an accidental circum- 

 stance arising out of the possession, for ordinary locomotion, of a 

 continuous supply of tenacious mucus. 



I " L.F.W. .Sliells in Norinamly," /• (V«</r., \o\. 5, 1SS6, p. 14. 



