INTRODUCTION 



It is customary to place all living beings in either the animal or 

 vegetable kingdoms, but in reality a sharp boundary line between 

 animals and plants first becomes possible when they exhibit a com- 

 plicated structure. In those of more simple organisation all distinc- 

 tions disappear, and it becomes difficult to define the exact limits of 

 Botany and Zoology. This, in fact, could scarcely be otherwise, as 

 all the processes of life, in both the animal and vegetaljle kingdoms, 

 are dependent on the same substance, protoplasm. With more 

 complicated organisation, the specific differences increase, and the 

 characteristics distinguishing animal from vegetable life become more 

 obvious. For the present, it must be confessed, the recognition of an 

 organism, as an animal or a plant, is dependent upon its corresj^ondence 

 with an abstract idea of what a plant or animal should be, based on 

 certain points of agreement between the members of each class. A 

 satisfactory basis for the separation of all living organisms into the 

 categories of animals or plants can only be obtained when it is shown 

 that all organisms distinguished as animals are in reality genetically 

 connected, and that a similar connection exists between all plants. 

 The proof of this can only be arrived at through the THEORY OF 



EVOLUTION. 



From the study of the fossil remains and impressions of animals 

 and plants, it has been established that in earlier epochs forms of life 

 differing from those of the present age existed on the earth. It is 

 also generally assumed that all living animals and plants have been 

 derived by gradual modification from previously existing forms. This 

 leads to the further conclusion that those organisms possessing closely 

 similar structure, which are united as species in a genus, are in reality 

 related to one another. It is also probable that the union of corre- 

 sponding genera into one family and of families into higher groups 

 serves to give expression to a real relationship existing between them. 



The presumable origin of a living organism from others previously 

 existing has been distinguished by Haeckel (^) as its phylogeny. 

 He termed the series of changes passed through by a living being in 



1 B 



