The terrestrial air-breathing mollusks of the United States, and the adjacent territories of North America
Year: 1851
Type: book
Abstract: All the species which have yet come under our notice possess the power of suspending themselves in the air by a gelatinous thread.This they effect by accumulating a quantity of tenacious mucus at the posterior extremity of the foot, which they attach to the object from which they are to commence their descent ; then, loosing their own hold, they hang suspended by this point.Continuing the secretion, their own weight attenuates the mucous attachment, and draws it out into a thread.As this dries and hardens, a fresh supply is afforded, the thi-ead is lengthened, and the animal lets itself down any desirable distance.At this time, also, the margin of the foot pours out mucus freely, and during the whole operation the locomotive disk is in active undulatory motion, in the same manner as when in ordinary progression.It appears in this way to guide and force towards the ex- tremity the mucus which is secreted on its surface, and which, collected at its extreme point, forms the thi-ead.The slug often pauses in its descent, and extends its tentacles and its whole body in various directions, as if seeking some object on which to make a lodgment.The faculty of suspending themselves in this manner indicates that they pass some part of their lives on trees, from which they can thus make a convenient descent to the earth ; there are some species, indeed, which are stated to inhabit trees almost exclusively.It may serve also as a means by which they can suddenly escape from the attacks of their enemies, and particularly of birds.It is mostly, however, when they are yoimg, or at least HABITS AND PROPERTIES.5 not grown to their full size, that they enjoy this power.Those which have attained their extreme dimensions and weight are too heavy to trust themselves to so frail a support.They have no power to elevate themselves again, and in this respect are inferior to the spiders, which can both lower and raise themselves by the aid of the secreted thread.Lilce the spiders, however, they often remain suspended in mid-air for a time, and it is not unlikely that there is some pleasurable sensation con- nected with the act, which induces them thus to prolong it.We have seen the descent actually practised by every one of our Atlantic species.Besides the watery fluid which at all times lubricates the integuments, the animals can, at their will, secrete at any point, or over the whole surface of their bodies, a more viscid and tenacious mucus than is usually exuded.This power is used as a means of defence.Whenever a foreign substance touches them, immediately a quantity of this mucus, of the consistence of milk and nearly of the same color, is poured out and forms a kind of membrane interposed between themselves and the irritating substance.So, also, when they are surrounded by a corrosive gas, or are thrown into water or alcohol, they form over themselves in this way a thick protecting cov- ering, which is undoubtedly a non-conductor of heat and impervious, at least for a time, to liquids.Shielded by this coating, they can live the greater part of a day immersed in water, and for a shorter time in alcohol ; and M. F^russac asserts that they have survived for hours in VOL.n. * As late as the close of the sixteenth century, Helling published a disser- tation with this title : " Ossicatlorum liviaciLTn itsiis in febrihits.''^* I employ in this instance the name selected by Dr. Binney, though both the names of Blainville and Buchanan have priority.g. VAGINULUS.
Authors: Amos Binney, W. G. Binney, Augustus A. Gould
Language: English
Subfield: Animal Science and Zoology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W623920102