314 GLANDULAR SYSTEM— -DERMAL CELLS AND SUPRA-PEDAL GLAND. 
Tlie glands discliargiiig e.\teriially are cliietly imicons, byssal, pig- 
nient and calcic glands, while the internal glands yield various products 
essential in the processes of digestion, reproduction and other })hases 
of animal economy. 
The chief mncons glands are the Ventral and Snpra-pedal glands, 
the Candal gland and the nyi)o-hrancliial gland, hnt, in addition to 
these more important organs, there are 
The Dermal Cells which are scattered plentifully over all the 
external surface of the body not covered by the shell, and ahundantly 
secrete a tluid mncus, which is clear and transparent in many si)ecies, 
hut tinged in others with pigment or may he obscured and rendered 
Kj(;. G()3. — Section ilirough a rugose glandular area of llie back of Helix poniatia L., showing 
tile scattered mucous and other cells, highly magnified (after Vogt and Vung). 
ch.c. lime cells filled with granular substance ; cp. epithelium ; in.^L mucous cells, some showing 
nuclei ; /. lacuna; ; nt. muscular fibres to skin. 
somewhat oj)a([ue by lime, which jireserves the integument in a cool, 
moist and supjjle condition, a state vitally essential to their very 
existence, desiccation of the skin being (piickly fatal. This dermal 
mucous secretion, especially of slugs, is also in some degree lu’o- 
tective, evidenced by the manifest distaste of its adhesive character 
shown by some of their enemies. 
The Anterior or .Supra-Pedal ({land, known also as the Sinus 
of Kleehurg and formerly considered as having an olfactory function, 
is a very important organ in the (lastntiiods, as it su])i)lies the luhri- 
Fig. G04. — 'I'estacella haliotidea Drap., X 2, laid open, the lingual diealh, with its powerful 
retractor muscles, turned outwards and the remaining viscera removed lo .show the position and 
general character of the Supra-Pedal Gland. 
l.s. lingual sheath : t.r. tentacular retractor of right side ; sp.g. supra-pedal gland. 
cant mucus for smoothing the path to he traversed by the animal and 
also assists t(j ensure the necessary adhesion to the objects upon or 
over which it may crawl. 
