4 INTRODrCTKtX. 



ill the proportion which these bear to onu anotlier in tlie organism thj\t animals 

 differ in any way from phdits. The most chai-acteristic of all vegetahlc coni- 

 ponnils is the one known as cellulose, very nearly allieil in its L-liemical com- 

 position to ordinary starch. As a general rule, it may he stated that the 

 l)resenoe of an external envelope of ccUnlose in any orgariism raises a strong 

 presnni])t.ion as to its vegetahle nature. 8tiil CL-Uulose is not exclusively con- 

 fined to plants, as was at one time hflieved. It is now well known that the 

 outer covering of the so-called Sea-squirts 'or Ascidiau MoUuscs contains a large 

 quantity of cellulose (as much as 60 per cent in sonte cases). Another highly 

 characteristic vegetable product is diJompliyU, the green colouring-matter of 

 plants. Any organism which exhildts chlorophyll in any quantity as a proper 

 element of its tissues is most prohalily vegetalile. In this case also, however, 

 the presence of chlorophyll cannot be regarded as a certain test, since it occurs 

 regularly in some undoultted animals {e.g., Stenlor amongst the hifasoria, and 

 the Hydra riridis, or gi'cen Fresh-water Polype, amongst the C< el enter ata). 



Fourthly, As regards lucomothe pou-tr, or the ability to effect changes of 

 jilace at will, the results of observation are singularly at variance with onr 

 preconeeiveii notions. Befure the invention of the microscope, no instances of 

 independent voluntary movements were known in plants, if we except the 

 voluntary opening and closure of flowers and their turning towards the sun, 

 the drooping of the leaves of sensitive plants under irritation, an<l some otlier 

 phenomena of a like nature,. Now, however, we know of many plants which 

 are endowed, either when young or throughout life, with the power of effecting 

 voluntary movements ajiparently as spontaneous nnd inde]iendent as those ex- 

 hibited by the lower animals. In sonu- r;isus 1lie nii'Veiiients are brought about 

 by means of little vibrating liairs or cilia, with which a part or the whole of the 

 surface is furnished. Wlien it is adiied that many animals are ])ermanently 

 fixed ami rooted to solid objects in tlieir fully-grown condition, it will be seen 

 that no absolute distinction can be drawn between animals and plants merely 

 on the ground of the presence or aTisence of independent locomotive po"wer. 



Fifthly, We have shortly to consider one of the most reliable of all the 

 tests by which an animal may be sejiarated from a plant — namely, tlie 

 nature e>f tlw fovd, and tlie jirodncts which are fonned out of the food within 

 the body. 



The ditferenoes between animals and iilants iu this rcspL-ct may be roughly 

 stated as follows :— 



1. Plants live ujion [nirely inorganic subsf ances, such as water, carbonic 

 acid, and amnnnna— and fhey have tlic }io\vcr of making, out of these, true 

 organic substances, s\icli as .stav<;h, cellulose, su.Liar, i!^c. Plants, therefore, 

 take as hiod M'l'v siniph- bodies, and ];ianiifacl me tlicm info much more com- 

 ]ilex substances, so that ]tlants arc the gn.'at pi'odiiccfs in nature. , 



2. All jdants which coidaiu .ljtccii cohiiii'ing-iiiattcr (.■hlorophyll) in the pro- 

 cess of digestion break up .■arbimic ai'id intn Ihc two elements of which it is 

 composed— namely, carbdn and oxy-cn. kee]iin,L: the cai'lioii and setting free 

 tlie oxygen. As carboinc acid ncciirs always in the air in small (]nantities, the 

 resvdt of this is that j)lants rennjve carbonic acid from the alinosphere ami cive 

 out oxygen. 



3. Animals, on the other hand, have no jMiwcrot !i\ing on inori;anic matters, 

 such as water, carbonic acid, anil aninionia. Tlicy have mi |.o\ver .if convcrtiiiir 

 tliese into the complex organic snbslaiiccs ul' uliicli llirir !)odies aiv eomposcd. 

 On the contrary, animals reqnire to be sn]i]ilied wil li rcady-niaile (iri,^anic cnm- 



