10 MANUAL OF ZOOLOGY. 



d. Afotor Power. — ^This, though broadly distinctive of ani- 

 mals, can by no means be said to be characteristic of them. 

 Thus, many animals in their mature condition are permanently 

 fixed, or attached to some foreign object ; and the embryos of 

 many plants, together with not a few adult forms, are endowed 

 with locomotive power by means of those vibratile, hair-like 

 processes which are called "cilia," and are so characteristic 

 of many of the lower forms of animal life. Not only is this 

 the case, but large numbers of the lower plants, such as the 

 Diatoms and Desmids, exhibit throughout life an amount and 

 kind of locomotive power which does not admit of being rigidly 

 separated from the movements executed by animals, though the 

 closest researches have hitherto failed to show the mechanism 

 whereby these movements are brought about. 



e. Nature of the Food. — Whilst all the preceding points have 

 failed to yield a means of invariably separating animals from 

 plants, a distinction which holds good almost without excep- 

 tion is to be found in the nature of the food taken respectively 

 by each, and in the results of the conversion of the same. The 

 unsatisfactory feature, however, in this distinction is this, that 

 even if it could be shown to be, theoretically, invariably true, 

 it would nevertheless be practically impossible to apply it to 

 the greater number of those minute organisms concerning 

 which alone there can be any dispute. 



As a broad rule, all plants are endowed with the power of 

 converting inorganic into organic matter. T\ie.foodoi plants 

 consists of the inorganic compounds, carbonic acid, ammonia, 

 and water, along with small quantities of certain mineral salts. 

 From these, and from these only, plants are capable of elabo- 

 rating the proteinaceous matter or protoplasm which consti- 

 tutes the physical basis of life. Plants, therefore, take as food 

 very simple bodies, and manufacture them into much more 

 complex substances. In other words, by a process of deoxida- 

 tion or unbuming, rendered possible by the influence of sun- 

 light only, plants convert the inorganic or stable elements — 

 ammonia, carbonic acid, water, and certain mineral salts — into 

 the organic or unstable elements of food. The whole problem 

 of nutrition may be narrowed to the question as to the modes 

 and laws by which these stable elements are raised by the vital 

 chemistry of the plant to the height of unstable compounds. 

 To this general statement, however, an exception must seem- 

 ingly be made in favour of certain fungi, which require organ- 

 ised compounds for their nourishment. 



On the other hand, no known animal possesses the power 

 of converting inorganic compounds into organic matter, but 



