COMPARATIVE ANATOMY. 



i. 



INTRODUCTION. 



ELEMENTS OF STRUCTURE. 



THE composition of all bodies is either inorganic or organic. 



An inorganic (mineral) body is homogeneous in structure, 

 and is either crystalline or without definite form. Its increase 

 results from external accumulation of particles. An organic 

 body is a product of organization. An organized body 

 (organism) is heterogeneous in structure, and has a definite 

 form. Its increase results from nutritive processes carried 

 on within. 



Every organized body is composed of ultimate and proxi- 

 mate physical elements. 



THE ULTIMATE PHYSICAL ELEMENTS are (1) homogeneous 

 liquid, as in the germinative area of the egg immediately 

 after impregnation ; (2) homogeneous granules, as in Monas 

 crepusculum ; (3) homogeneous filaments, as in cilia, sper- 

 matic filaments, and Vibrio; (4) homogeneous membrane, 

 as in basement membrane. (Leidy.) 



THE PROXIMATE PHYSICAL ELEMENTS result through union 

 of the ultimate elements. They are very constantly pro- 

 nounced in varieties of the organic cell, of which it is conve- 

 nient to speak, as an early, though not a primordial, expres- 

 sion of form. 



As usually described, the organic cell is a minute form, 

 composed of homogeneous membrane with intervening 



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