340 
MUSCULAR SYSTEM. 
basal portion of the gill and opening into the branchial vein, but 
a specialized area of connective cytogenons tissue, the Nephridial 
gland, invests the renal vascular plexus, and encloses lacunar spaces, 
which communicate with the auricle, the ammbocytes passing into 
the blood within its cavity. 
The amoebocytes and the large vesicular wandering cells, known 
as the “cells of Leydig,” take up and absorb sickly and degenerating 
tissue and foreign bodies wdiich have gained entrance into the system, 
indigestible or insoluble particles becoming encapsuled and removed 
from the circulation, a process of excretion which occurs in many 
animals; many of the mucus, pigment and other cells so numerously 
present in the external tissues are wandering cells, probably con- 
veying their contents towards the surface of the body, they also act 
as storehouses for the accumulation of a reserve store of nutriment 
in the form of glycogen. 
i\Iany of onr .species, owing to the energetic phagocytary action of 
their ammbocytes, can withstand, without apparent injury, the 
introduction into the body of many poisonous substances or large 
(quantities of bacterial disease germs. Our IleUx pomnt'ia\\&^ been 
demonstrated to successfully resist the deleterious presence of such 
organisms or substances within the body, the bacteria soon becoming 
collected together in the most delicate qmrts of the lung, which are 
essentially qdiagocytic in function. 
The Muscular System embraces the organs by which the move- 
ments of the body are accomplished, under the stimulus of the 
efferent nerves from the various ganglionic centres. 
This power of motion or movement is possessed by every animate 
creature, but in the lowliest organisms where there is little differentia- 
tion of i)arts, the whole body is mobile and contractile, constantly 
changing in shape by the inces,sant retraction or protrusion of different 
jiarts of the body substance in the form of Pseudopodia (\pevSys, 
false ; ~o8- foot) a qnimary form of movement exhibited by the 
ama'bocytes or white blood corpuscles, present in the blood of the 
mollusca and other animals. 
Cilia (ciliiim, an eye-lash) and Flagella (Jf<igelliun, a whip-lash) 
are finer and more delicate ju’olongations or extensions of the body 
std)stance, but imire i)ermanent in character; they form more advanced 
organs of loconnjtion, particularly cbaracteristic of the Infusoria and 
of the Wdiger and Trochosphere stages of the molluscan embryo. 
