34 DOCTRINE OF EVOLUTION 



imals undergo during the production of their final forms, 

 it is an independent study. Nevertheless we shall learn 

 how intimate are the relations of these two divisions of 

 zoology and how the evolutionary teachings of each body 

 of fact support and supplement those of the other. 



Palaeontology searches everywhere among the de- 

 posits of earlier ages for links to be fitted into their 

 proper sequence of time, from which it constructs the 

 chain of diverse types leading down to the species of 

 the present. A cat of to-day is therefore viewed in 

 an entirely different connection, as the last term in a 

 consecutive series of species. Forming alliances with 

 geology, and even with physics and chemistry, this 

 department of zoology endeavors to reconstruct the 

 past from what it learns to-day about organisms and 

 the conditions under which they live. Finally the 

 observations that cats of various kinds do not occur 

 everjrwhere in the world, but only in certain more or 

 less restricted localities, belong to the subject of geo- 

 graphical distribution, and illustrate its nature. 



Our task is to learn the teachings of these several 

 divisions by recalling and putting together what we 

 know already about the commonest animals, or noting 

 what can be observed in a visit to a zoological garden 

 and aquarium. On account of the present limitations 

 of time, the subject of classification will be combined 

 with comparative anatomy ; embryology will be taken 

 up together with these subjects ; palaeontology will be 

 the main subject of the next discussion, which will in- 

 clude also a brief statement of the meaning of dis- 

 tribution. Then we will be prepared to study nature 

 to see how evolution works. 



