THE MUSEUM. 



2r 



others we have simple threads or la- 

 mins r;/ jiving within the aperture in 

 the course of the spire. They are not 

 formed until the shell has attained its 

 full growth. 



The genera not furnished with an 

 external shell were grouped into one 

 family of Limacidce by Binney, who 

 thus describes their habits. They are 

 more especially nocturnal than the 

 other families of the order, and they 

 are so rarely visible in the day time 

 that thousands may be near without be- 

 ing known. The injury which they 

 commit in kitchen-gardens, for this 

 reason, is often vaguely ascribed to 

 worms or to birds, and no measures 

 are taken against the real culprits. 

 Their habits, in general, coincide with 

 those which have been described as 

 distinguishing the shell-bearing species, 

 and I shall therefore only mention 

 here, those which are peculiar to them. 

 They differ from the other families in 

 not possessing the faculty of hiberna- 

 tion, or suspension of their organic func- 

 tions during the cold season. In tem- 

 perate latitudes the snails hibernate, 

 under all circumstances, on the ap- 

 proach of cold weather; the slugs, on 

 the contrary having the power of resist- 

 ing extreme cold, continue in their 

 usual haunts until severe frosts set in, 

 when they retire into the earth and 

 other sheltered retreats. Here they 

 remain in a state of inaction and partial 

 torpidity; the functions of the body, 

 however, still going on, though slowly 

 and with diminished force. A slight 

 increase of heat arouses them and 

 stimulates the organs to renewed ac- 

 tion, and they accordingly often come 

 abroad in mild weather even during 

 the winter. Those which inhabit cel- 

 lars and other protected situations are 

 in motion throughout the year; and in- 

 dividuals of all the genera and species 

 which I have kept in confinement have 

 continued active, fed freely and in- 

 creased in size as much in the coldest 

 months as in the summer. 



All the species which have yet come 

 under my notice possess the power of 



suspending themselves in the air by a 

 gelatinous thread. This they affect by 

 accummulating a quantity of tenacious 

 mucous at the posterior extremety of 

 the foot, which they attach to the ob- 

 ject from which they are to commence 

 their descent; then, loosing their hold, 

 they hang suspended by this point. 

 Continuing the secretion, their own 

 weight attenuates the mucous attach- 

 ment, and draws it out into a thread. 

 As this dries and hardens, a fresh sup- 

 ply is afforded, the thread is lengthen- 

 ed, and the animal lets itself down any 

 desirable distance. At this time, a. so, 

 the margin of the foot pours out muc- 

 ous freely, and during the whole oper- 

 ation the locomotive disk is in active 

 undulatory motion, in the same man- 

 ner as when in ordinary progression. 

 It appears in this way to guide and 

 force towards the extremety the muc- 

 ous which is secreted on its surface, 

 and which collected, at its extreme 

 point, forms the thread. The slug 

 often pauses in its descent, and extends 

 its eye-peduncles and its whole body 

 in various directions, as if seeking some 

 object on which to make a lodgement. 

 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 conven- 

 ient descent to the earth; there are 

 some species, indted, which are stated 

 to inhabit trees almost exclusively. It 

 may serve also as a means by which 

 they can suddenly escape from the at- 

 tacks of their enemies, and particular- 

 ly 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 attain- 

 ed 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 spiders, 

 which can both lower and raise them- 

 selves 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 



