MORPHOLOGY OF ANIMALS 



radially symmetrical portions of the body, such as the 

 right and left arms and legs, each composed of several 

 systems and organs. 



Metameres (homo-dynamic parts) are serially symmet- 

 rical portions of the body, such as the successive somites 

 (segments) of the body of an earthworm or lobster, each 

 composed of many systems and organs. When the somites 

 are all alike they are said to be homonomous^ when they 

 differ one from another they are heteronomous, 

 (h) Persons are separate, distinct individuals, composed 

 of many or all of the preceding units, such as an earth- 

 worm, a frog, or a man. 



(d) Corms are groups of persons morphologically united, 

 such as a colony of sponges, hyroids, polyzoa, or ascidians. 

 (;) Societies are groups of individuals physiologically 

 united, such as a colony of ants, bees, or men. 



III. HOMOLOGY AND ANALOGY 



The general functions of living things, such as metabolism, 

 reproduction, sensitivity, are found in all plants and ani- 

 mals, but the various organs and systems by which these 

 functions are performed differ widely in different phyla. 



Analogy is similarity in function but not in structure. 

 Thus the wings of insects and birds are analogous, though 

 differing widely in structure. 



Homology is resemblance in structure and position, though 

 the function may or may not be similar. Thus the wing of a 

 bird, the fore-leg of a horse, and the arm of a man are 

 homologous, because they show fundamental resemblances 

 in position and structure, although they differ in function. 



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