ELEMENTARY BIOLOGY. 



INTRODUCTION. 



THE study of natural phenomena has occupied the atten- 

 tion of mankind from the earliest times of which we have 

 any record. That the observations so made should have 

 been crude, incomplete, and often erroneous, and that the 

 relationship of the several observations to each other should 

 have been, in most cases, entirely overlooked, are results 

 which are completely in accordance with what we know of 

 the development of scientific thought. For generalisations 

 appear late in the history of science, and, of necessity, their 

 advent is preceded by a period during which the efforts of 

 scientific workers are, consciously or unconsciously, directed 

 chiefly to the accumulation of stores of information on 

 matters of fact. Moreover, not only have those observations 

 already made to be revised, corrected, and extended, but 

 they require to be directly verified and amplified by ex- 

 periment before the generalisations or inductions formed 

 from their study can be said to be perfectly legitimate and 

 trustworthy. Observations previously isolated become aggre- 

 gated round these generalisations as centres, each generali- 

 sation being known as a natural law. 



The relationships discovered to exist between individual 

 phenomena were soon found to be capable of wide exten- 

 sion ; for the various natural laws which expressed these 



