iv THE ANIMAL KINGDOM. 



an elm-tree, a lily, or a fern, in having organs of sight, of hearing, of smell, of locomo- 

 tion, and special organs of digestion, circulation, and respiration, but these plants also 

 take in and absorb food, have a circulation of sap, respire through their leaves, and 

 some plants are mechanically sensitive, while others are endowed with motion — certain 

 low plants, such as diatoms, etc., having this power. In plants the assimilation of food 

 goes on all over the organism, the transfer of the sap is not confined to any one portion 

 or set of organs as such. It is always easy to distinguish one of the higher plants from 

 one of the higher animals. But when we descend to animals like the sea-anemones and 

 coral-polyps, which were called zoophytes from their general resemblance to flowers, 

 so striking is the external similarity between the two kinds of organisms, that the early 

 observers regarded them as ' animal flowers ;' and in consequence of the confused notions 

 originally held in regard to them, the term zoophytes has been perpetuated in works 

 on systematic zoology. Even at the present day the compound hydroids, such as 

 the Sertularia, are gathered and pressed as sea-mosses by many persons who are 

 unobservant of their peculiarities, and unaware of the complicated anatomy of the 

 little animals filling the different leaf-like cells. Sponges, until a late day, were re- 

 garded by our leading zoologists as plants. The most accomplished naturalists, 

 however, find it impossible to separate by any definite lines the lowest animals and 

 plants. So-called plants, as JBacterium, and so-called animals, as Frotamoeba, or 

 certain monads, which are simple specks of protoplasm, without genuine oi-gans, 

 may be referred to either kingdom ; and indeed, a number of naturalists — notably 

 Haeckel — relegate to a neutral kingdom (the Protista) certain lowest plants and 

 animals. Even the germs (zoospores) of monads and those of other flagellate infusoria, 

 may be mistaken for the spores of plants ; indeed the active flagellated spores of 

 plants were described as Infusoria by Ehrenberg ; and there are certain so-called flag- 

 ellate Infusoria so much like low plants (such as the red snow or Protococmts), in 

 form, deportment, mode of reproduction, and appearance of the spores, that even 

 now it is possible that certain organisms placed among them are plants. It is 

 only by a study of the connecting links between these lowest organisms, leading up to 

 what are undoubted animals or plants, that we are enabled to refer these beings to their 

 proper kingdom. 



" As a rule, plants have no special oj-gans of digestion or circulation, and nothing 

 approaching to a nervous system. Most plants absorb inorganic food, such as car- 

 bonic acid gas, water, nitrate of ammonia, and some phosphates, silica, etc., all of these 

 substances being taken up in minute quantities. Low fungi live on dead animal 

 matter, and promote the process of putrefaction and decay, but the food of these 

 organisms is inorganic particles. The slime-moulds called Ilyxotnycetes, however, 

 envelop the plant or low animals, much as an Amoeba throws itself around some living 

 plant and absorbs its protoplasm ; but the Myxomycetes, in their manner of taking food, 

 are an exception to other moulds. The lowest animals swallow other living animals 

 whole or in pieces ; certain forms near Amoeba bore into minute algse and absorb their 

 protoplasm ; others engulf silicious-shelled plants (diatoms and desmids) and absorb 

 the protoplasm filling them. No animal swallows silica, lime, ammonia, or j)hos- 

 phates as food. On the other hand, plants manufacture or produce protein in the 

 shape of starch, albumen, sugar, etc., which is animal food. Plants inhale carbonic 

 acid gas and exhale oxygen ; animals inhale oxygen and exhale carbonic acid ; though 

 Draper has discovered that, under certain circumstances, plants may exhale carbonic 

 acid. 



