i882. 165 Trans. N. Y. Ac. Sci. 



change of shape of the entire mass of the unicellular body. The power 

 of movement here resides in the unorganized protoplasm, without any 

 organs whatever. Even in the lowest form of life there is a conver- 

 sion of Vital force into Physical force. 



Higher in the animal scale we find motion by means of cilia. These 

 are minute elastic filaments which have a whip-like motion — alternate 

 flexion and extension. But the ciUa do not seem to be controlled ne- 

 cessarily by the creature's will. The motion is evidently automatic. 

 Many bw plants, as well as animals, have the body covered with cilia 

 by which they tumble about in the water very lively. In some of the 

 infusorians, however, the cilia seem to obey the animal's will. 



The means of motion in all higher animals is muscular tissue. This 

 is a highly specialized tissue, subjected to the nervous system, and 

 which concentrates the power of movement, which in the amoeba 

 was diffused through the whole mass of the body. Muscular power 

 resides in the contractility of the cells. Expansion of the cells or the 

 extension of the whole muscle is produced by elastic reaction— a 

 merely physical force —or by contraction of opposing muscles. Mus- 

 cles act under nervous, electric or other stimulus ; but sometimes no 

 stimulus seems necessary. 



The organs and methods by which the vital contractile force of 

 muscular tissue is utilized in producing mechanical power is a most 

 interesting study. [With the magic lantern a few of the more typical 

 and interesting methods of locomotion in animals were shown.] 



A few animals move without organs, as the sea-anemone in crawl- 

 ing or the jslly-fish, leech, and snake in swimming. But most ani- 

 mals have parts or organs specially adapted to locomotive purposes. 

 The old classification of swimming, flying and walking will answer our 

 purpose. 



Locomotion in water requires much less effort than locomotion in 

 the air, and more than locomotion on solids. But the organs tor swim- 

 ming are comparatively simple. The lobster swims backward by its 

 tail fin, which is a combination of beautiful oars. The squid swims in any 

 direction, by ejecting the water of respiration out of a flexible tube. 



Swimmers /ar excellence are the fishes. They propel themselves 

 chiefly by their tail fin, used as a horizontal scull oar. The remaining 

 fins are used to guide and control the motion. The paired fins are 

 based upon the arm and leg bones. The rays fly through the water by 

 means of the pectoral fins and side expansions of the body. The 

 whale propels himself by the vertical motion of the body and tail 

 Frogs, turtles, crocodiles and many birds are especially adapted to a life 

 in water. 



Locomotion in Air. — On account of the extreme rarity of the atmo- 



