92 



ON THE MUCUS-THREADS OF LAND-SLUGS. 



Bv II. WALLIS KEW. 



(Read before the Society, June 13th, 1900). 



For some time past the writer has been attempting to get together 

 the scattered information concerning tlie mucus-threads of slugs, 

 shell-bearing molluscs, planarians, etc.: animals of creeping locomotion, 

 ordinarily leaving a slime-film in their path. 



The phenomena presented, though not of wide importance, are of 

 some curiosity; and it is found that the threads in question, though 

 often merely of locomotory mucus, may yet serve for progression, 

 during descent or ascent, through air or water, and may be retraversed 

 by the animals. 



I have submitted a paper to the "Zoologist"' (ser. 4, vol. 4, p. 

 289-320, 1900) on the threads of shell-bearing molluscs and sea-slugs, 

 and to the "Naturalist" (1900, p. 307-317) on those of planarians; 

 and the present paper, from considerations of space, deals with land- 

 slugs only. It is mainly bibliographical; but I have ventured to detail 

 a few observations of my own, and have been permitted to give a few 

 others communicated by correspondents. P'or help with papers in 

 languages other than English, and in other matters, I am much indebted 

 to the kindness of Mr. G. K. (iude. 



PART I. 

 BIBLIOGRAPHY. 



1. Lister, M. Historije Animalium Angliae, 1678, p. 129-30. 



On one occasion, about the month of June, Lister observed slugs, 

 in dark woods, hanging from the branches of trees, each on a single 

 "thread, two feet long, made of their own slime. The animals per- 

 tained to the author's Liiiiax ci/ierens inaxiinus stria fits &^ niacitlatus : 

 our L. maximns or possibly L. arboru/n. 



2. Hoy, T. Account of a Spinning Limax, Trans. Linn. Soc, vol. 



I, 1 791, p. 183-5. 

 A slug was found su.spended from a Scotch-fir: 



It was hanging by one line only, which was attached lo its tail. This line or 

 thread at a distance of one inch and a half from the animal, appeared to be as fine 

 as those spun by the Aranea diadei/ia, but nearer to its body it was thicker; and, 

 at its junction to the tail, was broad and flat, exactly corresponding to the tail itself. 

 The Slug was four feet below the branch from which it was suspended, and at the 

 distance of four feet and a half from the ground ; to which it was approaching gradu- 

 ally at the rate of an inch in about three minutes, slower considerably than its ordinary 

 motion, either upon the ground or even in ascending the trunk of a tree, not so slow. 

 however, as one would expect, if it is considered that a slug is not furnished . 

 with a particular reservoir of glutinous liquid, . . . but that the line by M'hich it 

 descends, is drawn from that slimy, glutinous exudation gradually secreted from its 

 pores, and covering its whole Ijody. It seemed to require a great degree of exertion 



