GLANDULAR SYSTEM — MUCOUS FILAMENTS. 
‘Ml 
groove leading to tlie origin of the snspensoiy filament, and altliongli 
the mucus may become too thin to safely sustain the weight of the 
creature when gorged to repletion, yet when in need of food tlie 
mucus is more tenacious and becomes available as a ready means of 
transportation from one level to another. 
Fig. 608. Fig. 609. 
Fig. GOS. —Ar/on hoi'tensis F^r. descending by the aid of a slime thread. 
Fig. ()0n. — Arion suhfusctirS Drap., young, re-ascending by means of a slime thread, which it 
had previously descended. 
(Modified from original sketches by Mr. H. Wallis Kew, F.Z.S.) 
It is, however, principally by the immature animals that this 
method of locomotion is indulged in, as when full size and weight is 
attained this method of progression is not so essential and becomes 
more precarious and uncertain. 
The same mucous filament can also be made use of, if necessary, to 
re-ascend to the point of suspension, this being accomplished by bring- 
