HABITS AND FACULTIES. 



13 



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 young, or at least 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 them- 

 selves again, and in this respect are inferior to the spiders, which can 

 both lower and raise themselves by the aid of the secreted thread. Like 

 the spiders, however, they often remain suspended in mid-air for a time, 

 and it is not unlikely that there is some Fig. l. 



pleasurable sensation connected with the 

 act, which induces them thus to prolong 

 it. We have seen the descent actually 

 practised by every one of our Atlantic 

 species, as well as by the large Pacific 

 Arlolimax. 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 cor- 

 rosive gas, or are thrown into water or alcohol, they form over them- 

 selves in this way a thick protecting covering, 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 im- 

 mersed in water, and for a shorter time in alcohol ; and M. Ferussac 

 asserts that they have survived for hours in boiling water. They leave 

 a trace of their usual secretion on every object over which they pass, 

 and thus can easily be traced to their retreats. The ordinary secretion 

 is most abundant at their posterior extremity. The secretion of the 

 mucous fluid over their surface is necessary to their existence. Death 



Limax campestris, suspended. 



