HELIX — GLANDULAR SYSTEM. 
157 
Helix aspei'sa, like other mollusca, has little proper heat, and is 
practically Poikilothermic or approximately of the same temperature 
as the surrounding atmosphere, hecomiug colder or warmer internally 
in accordance with, and in response to the variations of temperature 
to which it is exposed. The contractions of the heart are more 
numerous in the young than in the adult mollusk under similar con- 
ditions, hut the number of pulsations has a wide diurnal range and in 
our ordinary summer temperatures probably varies between twenty- 
five and sixty-five per minute, even in the same animal, as the action 
is intimately related to the external temperature, being accelerated 
by increased warmth or active movement and diminished by cold, 
under which latter circumstances the contractions become more feeble, 
with however an occasional beat of full amplitude. 
The Glandular or Secretory system, with which are included the 
e.xcretory organs, are constituted of those organs or glands l)y which 
substances differing in composition from the blood and necessary for 
the proper exercise of the functions of the body are elaborated there- 
from and utilized, or if hurtful expelled 
from the system. It is composed not 
only of the salivary and digestive glands, 
which assist in the processes of digestion, 
and the digitate, albumen, prostatic and 
other glands, which are adjuncts to the 
reproductive organs and are alluded to 
under the systems with which they are 
functionally connected, but the whole 
surface of the body, foot and mantle is 
more or less glandular and furnished with 
unicellular glands, of which those con- 
taining pigment give the surface of the 
body or its various organs their charac- 
Fig. 320. — Portion of Corium and 
Cuticle of back of llelisc poinatia^ 
highly magnified (after Flemming), 
to show its structure and glandular 
nature. 
C't.c. connective tissue cells, with 
interspersed nuclei, n. ; ep.c. cylin- 
drical epithelial cells ; h.c. hair cells ; 
in. longitudinal and cross cut muscle 
fibres ; /. pigment ; s.g^. slime or 
mucous glands. 
teristic colour. There are also numerous mucus cells scattered over 
the whole surface, which maintain the exterior in a moist and pliant 
condition. A very dense aggregation of such cells exists within the 
Pedal gland, a medial supra-pedal invagination, which extends back- 
ward within the foot and opens anteriorly by a cleft between the 
mouth and foot; the contained glands secrete mucus abundantly, 
which is expelled by the aperture in advance of the foot and serves 
to lubricate the path to be taken by the mollusk. 
