30 CHAPTERS ON THE NATURAL HISTORY 



solid food, if of a suitable composition, to the liquid state. And 

 not merely is there a difference of this kind in the mode, there is 

 also one no less important, although less general, in the mate- 

 rials of nutrition. While under present terrestrial conditions 

 those substances, or chemical combinations, which are required 

 for the nutrition of animal organisms are, as far as we know, 

 nowhere spontaneously produced — that is to say, nowhere apart 

 from the influence of living organisms — materials derived wholly 

 from the inorganic world are sufficient to sustain directly nearly 

 the whole of vegetable life, and, therefore, indirectly, of all other 

 life as well." As thus differentiated, then, we leave the dealing 

 with vegetable life and plant-forms of every description to the 

 consideration of the vegetable physiologist and the vegetable 

 morphologist — to the botanist in the widest sense — and briefly 

 take here into consideration only scientific classificafory methods 

 as applied in the animal kingdom, though it may be said the same 

 principles obtain in both. In biology, the term taxonomy is now 

 frequently employed for the word classification. Each signifies 

 the same thing, however — to fix objects or material in some defi- 

 nite order; to arrange them, or it, according to some defined plan 

 adopted for the purpose. 



In all classifications we base our arrangements upon the re- 

 semblances (homologies) or non-resemblances of the things clas- 

 sified. 



Biological classification follows the same course, and, in it. it 

 is the structure of the forms under consideration that is taken 

 into account. The structure of animals constitutes the science 

 of morphology. But morphology means nothing more than what 

 we formerly comprehended by the term anafomi/. Anatomically, 

 the structure of organic forms is considered along two more or 

 less distinct lines; the one being "gross anatomy," or all that 

 pertains to the consideration of organs and parts in their en- 

 tirety; the other being "minute anatomy," or histology, wherein 

 the use of the microscope is essential to its prosecution, and the 

 province of its department being the examination and compari- 

 son of the ultimate structural detail of organs and other parts. 



Topographical anatomy treats of the external form and parts 

 of animals, and may be studied upon the living specimens; that 

 branch of anatomy dealing with the internal parts usually being 

 undertaken only upon the dead bodies of animals. 



