8 MANUAL OF ZOOLOGY. 



secreted by the liver of the Mammalia, is closely allied to, if 

 not absolutely identical with, the hydrated starch of plants. 



d. Motor Poiuer. This, though broadly distinctive of 

 animals, 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 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 

 exception 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 dis- 

 tinction is this, that even if it could be shown to be, theoreti- 

 cally, 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. The food of 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 

 elaborating the proteinaceous matter or protoplasm which 

 constitutes the physical basis of life. To this general state- 

 ment, however, an exception must seemingly be made in 

 favour of certain fungi, which require organised compounds 

 for their nourishment. 



On the other hand, no known animal possesses the power 

 of converting inorganic compounds into organised matter, 

 but all, mediately or immediately, are dependent in this re- 

 spect upon plants. All animals, as far as is certainly known, 

 require ready-made proteinaceous matter for the maintenance 

 of existence, and this they can only obtain in the first instance 

 from plants. Plants, therefore, are the great manufacturers 

 in nature, animals are the great consumers. 



Just, however, as this law does .not invariably hold good for 

 plants, certain fungi being in this respect animals, so it is 



