GLANDULAR SYSTEM — MUCOUS FILAMENTS. 
31 S 
ing tlie extremities of tlie body together and transferring the point of 
attaclnnent of the snsjjonsory tilainent from the tail to tlie head, the 
tilanient re-traversed in ascending being accumulated as an irregular 
mucous mass near the tail. The mucous tilanient has been ascertained 
by iMr. T. lloy to he produced by Ltmud' filaiis, a variety of Agrioliiii'tx 
agn'sfls, at the rate of one-third of an inch per minute, while in regard 
to its possible length iMr. II. Growtlier, in August, 1S90, at Truro, 
observed a specimen of the .same sjiecies in the act of descending from 
the branch of an elm tree twelve feet from the ground, the slug when 
ohserveil having already descended seven feet of this distance. 
Some Limaces have also been observed to use this power of pi’O- 
ducing mucous threads during .sexual congre.ss, spirally coiling around 
each other’s bodies and su.sjiending themselves heads downwards 
during that function by means of a jointly produced mucus cable. 
The tluviatile mollusks, owing to the greater density of ivater, are, 
however, the greatest adejits at this mode of travelling, the Pliysinai, 
and especially Aplecta hyp- 
noram, making free use of 
this interesting mode of pro- 
gres.sion, and readily forming 
upwardly or downwardly 
directed mucous threads of 
considerable length, athxing 
them between ditferent points 
where they may remain in 
liosition fur a length of time 
and become thickened and 
strengthened each time of 
ii.sage by the adhc.uon of the 
him of iiincns left behind h)' 
each .snail using the hlament. 
These hlaments,when hxed, 
offer a convenient and direct 
means of access to the surface 
for respiratory imrposes or ])ermit an ea.sy descent into the depths 
when the Inng cavity is inflated with air and the animal and its .shell 
thus rendered lighter than the n-ater, into nhich it can only enter by 
expelling a portion of the uir contained in the Inng-sac or by crawling 
down a hxed hlament, the stem of a plant or other suitable object. 
Fid. GIO.— Suspensory mucous filament alTi.ved to 
water surface aiul formed by Liuuuea auyicitlaria 
(L.) in the aquarium. 
