SheUs. 
S.A, fiCAT.. VOL. Xir. 
F<0eRtMRY, 1933. 
>/ 
SHELLS. 
By BERNARD C. COTTON. 
(Civea in the form of a lecture to this Society on the evening 
of November 15th). 
Almost everyone has seen and admired tlic beautiful shells 
found on sea beach.es. ft is about the structure of these 
and their relati\'es this article is written. 'I’he animals which 
make the shells are soft-bodied creatures Avithout bones and so 
they- are called Molhisca from the Latin mollis - soft. They are 
divided into four different groups. 
First!}', the Pelecy [>oda (meaning 'ktxe-footed’'), a represen- 
tative of which is t!ie cockle. Secondly, the Cephalopoda (mean- 
ing *‘head-footed”). for instance, the cuttle-fish and octopus. 
Thirdly, the Gastropoda (meaning “belly-footed”), with spiral 
shells like the periwinkle. Fonrthlv, the Scaphopoda (meaning 
“scoop-footed”), or the tusk shells which have a scoop-like foot 
at the wider end. 
Tilt* cockle may be compared with a book standing slightly 
open Ott a table hinge uppermost (hg. lA, 13.) 
Fig. I. ^.—Section of a book. B . — Section of a Cockle. 
The backs represent the shell; the hinge, the hinge of the 
shell; the leaves the gills. The gills procure oxygen for the animal 
from the current of sea-water in winch they are bathed. The}' also 
act as filters to obtain the minute life which is the cockle’s food. 
The gills are so constructed as to present the greatest possible 
surface to the ox\geiiating sea-water — just as our lungs form a 
large surface exposed to the inhaled air. A small section of the- 
gill (fig. 2) looks something like the radiator of a car, and. in 
fact, has a similar function, only the radiator exposes a maxinuur- 
surface to the air for cooling the water it contains. 
