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212 HELIX POMATIA. 
Description.—ANIMAL large and bulky, usually of a pale yellowish-grey or 
cream colour, more or less dusky, with large and prominent TUBERCLES, which 
diminish in size and prominence towards the mantle and the extremities of the 
body, and are separated by grey interstitial spaces ; UPPER TENTACLES or omma- 
tophores very long, clear greyish-yellow, beset with small rounded granulations, 
and each terminating in a moderately bulbous extremity, bearing the small but 
distinct black EYE-SPOT ; the LOWER TENTACLES are wide apart, and tinged with 
brownish at the free ends; the MANTLE is of a clear yellowish or creamy tint, 
extending slightly beyond the shell margin in crawling and showing three lobular 
extensions, one being the columellar lobule, while the others are near the RESPIRA- 
TORY ORIFICE ; FOOT ample, obtuse in front, and tapering behind to a fine point. 
SHELL globular, thick, solid, and opaque, conically-convex above, and rounded 
beneath ; SPIRE composed of five convex whorls of a yellowish- or whitish-grey 
colour, with a brown epidermis or PERIOSTRACUM, which is very deciduous, and 
usually showing three or four somewhat indistinet brownish bands, though ocea- 
sionally the five bands characteristic of the Pentatenia are present ; the surface is 
also irregularly ridged by the lines of growth, and bears a number of somewhat 
indistinetly incised spiral lines; APEX or nuclear whorl smooth; SUTURE deep 
and distinct ; UMBILICUS oblique and partially concealed by the thickened and 
reflected columellar margin. APERTURE oblique and broadly lunate, with a thiek- 
ened, slightly reflected PERISTOME. The EPIPHRAGM which closes the aperture 
during hibernation is thick, opaque, greyish-white, and cretaceous, convex exteri- 
orly, and formed of many closely-adherent layers. The epiphragm is appreciably 
less mineralized than the shell, being composed, according to an analysis by Mr. 
H. Crowther, of 93°16 per cent. of caleareous matter and 6°83 per cent. of organie 
substances ; while M. Delacroix gives 28-03 per cent. of carbonate of lime, 14°77 
per cent. of other mineral substances, and 57°20 per cent. of organic matter. 
Alt. 45 mill. ; diam. 45 mill.; average weight of adult shells about 90 grains. 
INTERNALLY, the 
NERVE RING shows a 
evreat concentration and 
fusion of the medullary 
ganglionic masses and a 
consequent obliteration 
of the commissures con- 
necting them. The pyri- 
form CEPHALIC GANGLIA 
are so closely connected 
that the commissure is 
only indicated by a slight Fic. 274. Fic. 275. 
median contraction or Fic. 274.—Nerve ring of Helix pomatia, enlarged (atter Moquin- 
narrowing, while the Tandon), showing the cephalic and visceral ganglia and connectives. 
VISCERAL eroup is fused Fic. 275.—Heart of Helix pomatia, X 4. a. auricle; v. ventricle. 
into one mass, joined by stout connectives to the SUPRA-GESOPHAGEAL group. 
The organs of special sense are well developed, the AUDITORY! or equilibrating 
organs being placed as usual on the surface of the pedal ganglia and containing a 
large number of flatly-oval OTOCONIA, of concentric and radial structure, though 
otoconia of other shapes are occasionally found. 
Fic. 276. BiG. 277. 
Fic. 276.—Front and side view of an otoconium of Helix pomatia, highly magnified (after Leydig). 
Fic. 277.—Unusual forms of otoconia from the otocyst of //. pomatia, highly magnified (after Schmidt). 
Fic. 278.—Alnormal forms of the digitate mucus glands of Helix fomatia, from Reigate (enlarged). 
The EYES? are placed near the tips of the dorsal pair of tentacles, and possess 
many of the essential constituents of the human eye, a crystalline lens, retina, ete., 
being present, but the optic nerve enters behind and not as in man, and thus there 
1 Monog. i., p. 150, f. 310. 2 Monog. i., p. 159, f. 311, 
