IX'I'UDDITTIOX. 3 



the kindred sciences of Zoology and Botany. It might have Ijeen 

 thought that notliing could be easier than to determine the animal 

 or vegetable nature of any given organism ; and such, indeed, was 

 the almost universal belief of older observers. In jioint of fact, how- 

 ever, no hard-and-fast line can be drawn, in the present state of our 

 knowledge, between the animal and vegetable kingdoms, and it is 

 often a matter of e,x;treme difficulty, or even wholijr impo.s.sible, to 

 decide positively whether we are dealing with an animal or a ])lant. 

 In the case of the higher members of the two kingdonrs there is no 

 difficulty in arriving at a decision. The higher animals are readily 

 separated from the higher plants by the jiossession of a distinct 

 nervous system, of locomotive power which can be voluntarily exer- 

 cised, and of an internal cavity fitted for the reception and digestion 

 of solid food. The higher plants, on the other hand, possess no nerv- 

 ous system or organs of sense, are incapable of voluntary changes of 

 place, and are not provided with any definite internal cavity, their 

 food being wholly fluid or gaseous. 



The lower animals {Protozoa) cannot, however, be separated in many cases 

 from tlie lower plants {Protopkytu) liy these distinctions, since many of tlie 

 former have no digestive cavity, and are destitute of a nervous system, and 

 many of the latter possess the power of active locomotion. In determining, 

 therefore, the nature of these amhignons organisms, the following are the chief 

 points to be attended to :— 



Firstly, As to mere_/(>?'»i or extern.al configuration, no certain rules can be 

 laid down for separating animals and plants. Many of the lower jilants, either 

 ia their earlier stages of existence or when grown np, are exactly similar in 

 form to some of the lower animals. This is the case, for e.xaniide, in some of 

 the Algce, wliich closely resemble some of the Infusorian animalcules. Many 

 undoubted animals, again, are rooted to solid oVijects in their adult state, and 

 are so plant-like in appearance as to be always popularly regarded as vegetables. 

 This is the case with many of the so-called Hydroid Zoophytes, such as the Sea- 

 firs, and also with the much more highly organised Sea-mats [Fhistra], all of 

 wliicli are usually regarded as sea-weeds by seaside ^-isitors. Tliis is also, but 

 less strikingly, the case with the Corals and Sea-ancmoues, of whi(di the latter 

 are often spoken of as *' sea-Ilowers." 



Secondly, No decided distinction can be drawn between animals and plants 

 as to their minute internal structure. Both alike consist essentially of nnnute 

 r>olid particles (molecules or granulesl, of cells, or of fibres. 



Thirdly, As regards chemical covqMsition, there are some decided, though 

 not universal, differences between plants and animals. As a general rnle, it 

 may be stated that plants exhibit a decided predominance of what are known 

 to chemists as "ternary compounds" — th.it is to .say, compounds which, like 

 suo-ar, starch, and cellulose, are composed of the three elements, carbon, hydro- 

 gen, and oxygen. They are, comparatively .speaking, poorly supplied witli 

 "quaternary" compoumls, which contain the fourth element, nitrogen, iu 

 addition to the three first mentioned. Animals, on the otlier hand, are rich in 

 quaternary nitrogenised comiiounds, such as albumen or filirin. Still, in lioth 

 kingdoms we find nitrogenised and non-nitrogenised conipo\UKls, and it is only 



