CIRf'ULATORY SYSTEM — PERICARDIUM AND HEART. 
280 
M'ere cultivated plants and 4 were fungi, and only the residuary 1 1 
M'ere M’ild phanerogamic plants, but 6 of these were not very freely 
eaten and not one was devoured with that avidity which characterizes 
snails when really pleasant food is offered, for at such times they con- 
sume enormous quantities, eating the night through without inter- 
mission, AgrioUmax agrestis having been known to devour one-third 
its own weight within twenty-four hours, and when we see the destruc- 
tion \vi-ought amongst plants defended in such various ways, we must 
conclude that many would soon be entirely extirpated if the barriers 
to their fi’ee consumption were removed. 
The Circulatory or Vascular system, known also as the Ilreinocad 
(af/xa, blood ; KotA-os, liollow), is greatly developed in the mollusca, 
and consists of blood vessels and .sinuses, shut off from the general 
digestive cavity, of v’lich it may, however, be regarded as an adjunct, 
as it is the medium by which nutriment is absorbed from the alimentary 
canal and carried to all parts of the body. 
A portal circulation is constituted by that portion of the .systemic 
circulation of the blood which flows to and circulates within the 
kidney or renal organ prior to entering the auricle. 
The Pericardium (vre/u', around ; KapSia, heart) is a thin-walled 
.sac, often thick and glandular in front, which contains or encloses 
the heart, and is partially embraced by the renal organ. It is con- 
stituted by an isolated jiart of the secondary body cavity or coelom, 
who.se epithelial lining also extends over and covers the exterior of 
the heart. The pericardial cavity receives the acrid secretion of the 
pericardial gland which is passed from the system by way of the 
reno-pericardial funnels. 
The Heart is the central and chief blood vessel, and is a dorsally 
placed contractile organ, symmetrical and median only in Pelecypods 
and in the most archaic Gastropods. 
In those Gastropods whose viscera 
have been most modified in position 
by the torsion and subsequent 
partial detorsion the body has 
Fig. 572. — Heart of Helix 7>irgata i ,11 , • i . n 
Da Costa within the opened pericardium and linClGrg'OllG, tllG llGtirt, lU tlGXtralJy 
also showing the close apposition of the renal •! i • t • i 
organ or kidney. C011G(1 llUllVldlUXls pOSSGSSlllg' a FG- 
a. auricle; 7C ventricle; k. kidney or • , ♦, ♦.tip 
renal organ. spiratory cavity, OCCUplG.S tllG iGit 
anterior side of the body, but is placed at the right side in sinistral 
specimens, and it is only when detorsiou is complete that the heart 
25,10,99. 
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