Quarierly Journal of Concliology. 407 



\\here they feed upon jxarticles of decaying vegetable matter, 

 this property of thread-spinning seems admirably suited to their 

 requirements. 



It enables the Slugs to descend from considerable heights, 

 as from branch to branch of a tiee, quicker and easier than by the 

 process of creeping. 



Messrs. Binney and Bland*' describe, I think very correctly, 

 the use of the thread to the Cydophoridce — "As the operculum 

 prevents the animal, when at rest and retired within its shell, from 

 adhering by means of its foot, as is usual with the HcUcido:,-\ the 

 animal has the power of spinning a short thread, which is attached 

 to the object of support. By this it hangs suspended at pleasure." 

 Among the Pectinibranchs, it enables the snail to reach the 

 bottom gently, instead of falling roughly or suddenly. It serves 

 the same purpose among the Nudibranchs.j 



The SphaeridjE, through their capability of climbing and float- 

 ing, in which exercises they are fond of indulging, especially when 

 young, are enabled to enjoy a more extended range of habitat and 

 food ; and when during their excursions they desire to rest, this 

 mucus-cable (always short, generally hardly to be spoken of as of 

 any length, but simply a mucous attachment) keeps them safely 

 moored, while, with foot and siphons withdrawn, they take a short 

 period of repose. 



* " Land and Fresh-water Shells of North America, part iii, p. 96, 

 Washington Smithsonian Institution, September, 1865. 



f When a Helix wishes to attach its shell some distance from the ground, 

 to a wall or tree, its method of procedure is interesting and curious. — Ilavino- 

 attained the desired spot, it shrinks itself partly within its shell, leaving only 

 the foot, which is shrunken, projecting; it then exudes mucus from the edrres 

 of the mantle, which becomes attached to the object of support and to the ed^e 

 of the mouth of its shell, it then withdraws further into its shell, leaving only 

 the tip of the posterior end of the foot attached, remaining thus until the film 

 of mucus has hardened, when it withdraws entirely into its shell. I have 

 observed this many times, both in English and North American Helices. I 

 have not seen a Helix or a Biiliiiii/s use a thread in any way. 



+ Alder and Hancock, "Monograph of the Nudibranchiate Molhisca." 



