AUXILIARY ORGANS — EPIPHRAGM. 
129 
Daubenton was the first to notice tliis remarkable appendage, but 
jMiiller gave the first full and accurate account of its function and 
structure under the names of Ossicula and Scala. Draparnaud in LSOl 
and Miller in 1822 independently discovered and described it, ap- 
parently in ignorance of the work of their predecessors. 
The Epiphragm (eVt, upon; c^pdy/xa, protection) or Ilybernaculum, 
as it is sometimes called, is another means of protection to the 
animal when enclosed in the shell, though differing essentially from 
both the operculum and the clausium, as the former is permanently 
attached to the animal and the latter permanently fixed to the shell, 
while the epiphragm has no organic connection with either the shell 
or animal. The epiphragm presents neither appendages nor incre- 
mental marks, as in the clausium and operculum, and is only 
temporarily adherent to the shell, from which it is cast off and 
renewed as often as the animal’s necessities require. 
According to Biuney, when the mollusk desires to form an 
epiphragm, it withdraws within its shell, and brings the collar of the 
mantle to near the level of the aperture, exuding therefrom a 
quantity of mucus, more or less intermingled with calcareous particles, 
sufficient to cover the exposed surface ; the mucous pellicle is then 
detached from its adherence to the animal by a small quantity of air 
emitted from the respiratory orifice, which projects the film into a 
convex bubble-like form, the animal at the same moment shrinking 
further within the shell, and the external air forcing the delicate 
epiphragm to a fiat or even concave shape ; it then hardens and 
becomes fixed to the inner margin of the aperture of the shell. All 
these actions are almost instantaneously effected by the animal. 
The epiphragm is composed of the mucoid secretions of the animal, 
mingled with calcareous granules, some of which exhibit a concentric 
structure ; it is permeable to air and 
not softened by or soluble in water and 
varies very greatly in character not only 
according to the species, but even in the 
same individual, according as to whether 
it is secreted for protection during the 
winter dormancy or merely to prevent 
the drying of the tissues during diurnal 
repose or enforced abstinence. The diurnal or summer epiphragm is. 
Fig. 287 . — Helix ne7noral{s L. 
Castle Hill, Scarborough, 
Showing in sitfi the thin, iritlescent 
diurnal or summer epiphragm, with 
the white calcareous thickening in 
front of the respiratory orifice. 
I 
