INTRODUCTION. 



1. All living beings are said to Two 



belong either to the Animal or Vegetable Kingdom, in other Bi p lo 8 ical 

 words they are classed, respectively, as Animals or Plants. 

 Biology is a term applied to the study of all living beings, 



i.e. of both animals and plants, The two biological sciences 

 are Zoology and Botany, the former embracing the study of 

 animals, the latter that of plants. 



2. So long as we confine our plants and 



attention to those highly organised forms of life which Animals, 

 have an elaborate and complicated structure we find no 

 difficulty in distinguishing the members of the two natural 

 kingdoms. Hence, in early times, when the total number of 

 plants and animals known to scientists was comparatively 



small while those which were known belonged to the 

 higher forms, a definite line of distinction could be easily 

 drawn between them. With the progress of time knowledge 

 has gradually extended, and with the help of the microscope 

 we have gradually passed from a consideration of the large 

 and obvious to a study of the minute and formerly invisible 

 things of life, and we are now aware of the existence of a 

 number of simple forms of life to which the ordinarily ac- 

 cepted notions of what constitutes an animal, or a plant, fail to 

 apply and which, in consequence, we cannot classify as either. 

 The study of such forms which stand at the bottom of the 

 scale drives us to the conclusion that no definite boundary line 

 can be drawn between the Animal and Vegetable Kingdoms, 

 and it should be borne in mind that the substance which con- 

 stitutes the basis of life, viz. protoplasm, is essentially the 

 same in both animals and plants. With the exception of such 

 simple forms, however, there is generally a great difference 

 between the members of the two kingdoms, and it is obviously 

 convenient for the purpose of study to keep them separate. 

 Animals, then, as compared with plants, usually have more 

 independence of action, while perhaps the mo&b characteristic 

 distinction of the majority of plants consists in the fact that 

 they possess a green colouring matter called chlorophyll (a 

 word which means leaf -green), by means of which they are 



