4 LIMACID^E. 



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 thread 

 is lengthened, and the animal lets itself down any desira- 

 ble 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 thread. 

 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 young, or at least 



