GLANDULAR SYSTEM. 
813 
rough walls to reach some favourite food, and when satiated not 
retiring at daybreak to the shelter of any convenient crevice, as might 
be supposed, Imt almost invariably retracing its often toilsome and 
arduous way to reach its favourite shelter, a peculiarity that has been 
verified by many observers on numerous occasions. 
I’he complex tracks formed by the nocturnal foraging expeditions 
of Lhnax maximns, L.^ffavus, and jorobably other species, which are 
sometimes so readily traced by the mucous trails they leave behind, 
also very frecpiently describe tlie double-loo}) or figure of 8 already 
mentioned, as distinguishing the track of Patella vulgata. 
Fig. 602. — Mucous track of Limax Jlai’us L., 19 feet in length, as observed by Mr. H. Wallis 
Kew, F.Z.S., on a flagged garden path at Louth, Lincolnshire. 
Mr. Lionel E. Adams at my re(piest kindly made many careful 
diagrams of limacidian tracks at Ashbourne, Derbyshire, and these 
almost invariably formed the same peculiar figure. The animals on 
setting out are probably guided by the olfactory sense as to the course 
pursued, but make a wide sweep upon the return home, and usually, 
though not invariably, cross the outward track at some point before 
again reaching the desired haven. 
The Glandular .system is a well-developed and specially charac- 
teristic feature of the molluscan organism. 
A gland is constituted by a collection or aggregation of simple 
secretory cellules which separate or elaborate frtjm tlie blood certain 
products, which may be utilized in physiological processes or, if 
noxious, can be speedily expelled from the body. 
