36 COMPARATIVE ANATOMY. 



V. 



APPAKATUS OF MOTION, 



THE movements of animals are effected by sarcodous or 

 ciliary action. 



SAKCODOUS ACTION. Due either to presence of sarcode or 

 muscular tissue. 



Sarcode. This is a gelatinous, diaphanous, contractile 

 substance, occurring abundantly in larvse of insects, embryos 

 of vertebrates, worms and radiates. (Griffith, Micrograph. 

 Diet.) 



It constitutes nearly the entire body in the Rhizopoda; 

 and with them carries on all the nutritive processes. With 

 such its contractility enables it to modify, from time to 

 time, the form of the animal. Thus in the Amceba, from 

 the alternating contraction and dilatation of portions of the 

 sarcode, the shape of the animal is constantly varying. 



Progression is effected by the protrusion of portions of the 

 sarcodous mass from the sides of the organism, forming 

 foot-like processes (pseudo-podia). These may be made to 

 adhere to some adjacent object, and the body slowly drawn 

 toward the point of attachment. Under certain circum- 

 stances Amdba protrudes its pseudo-podia at one extremity 

 of the animal immediately in advance of the contractile 

 vesicle. 



The motion of an embryonic mass within its egg capsule 

 before any differentiation of tissue is seen, is perhaps com- 

 parable to that of sarcode. 



Muscular Tissue. This is a peculiar contractile substance 

 resembling sarcode, arranged within tubular sheaths. A 

 single sheath with contents constitutes a fibrilla, a collection 

 of fibrillse, a fibre, and a bundle of fibres, a muscle. 



The primary elements of muscular tissue in a state of de- 

 composition possess independent motion. (Clark.) 



Every muscle being in relation to one or more movable 



