ON BIOLOGY. 53 



forms by descent and variation completely changes the 

 aspect of the question, and invests the facts of distri- 

 bution with special importance. The time when a group 

 or a species first appeared, the place of its origin and the 

 area it now occupies upon the earth, become essential 

 portions of the history of the universe. 



"The course of study initiated and so largely developed 

 by Mr. Darwin has now shown us the marvelous inter- 

 dependence of every part of nature. Not only is each 

 organism necessarily related to and affected by all things, 

 living and dead, that surround it, but every detail of 

 form and structure, of color, food, and habits, must it 

 is now held have been developed in harmony with, and 

 to a great extent as a result of, the organic and inorganic 

 environments. Distribution becomes, therefore, as es- 

 sential a part of the science of life as anatomy or 

 physiology. It shows us, as it were, the form and struc- 

 ture of the life of the world considered as one vast 

 organism, and it enables us to comprehend, however im- 

 perfectly, the processes of development and variation dur- 

 ing past ages which have resulted in the actual state of 

 things. 



"It thus affords one of the best tests of the truth of our 

 theories of development; because the countless facts pre- 

 sented by the distribution of living things in present and 

 past time must be explicable in accordance with any true 

 theory, or, at least, must never directly contradict it." 

 (Wallace, Art. Distribution, Brit. Encyclop., 9th Ed. V. 

 VII, p. 267.) 



These truths, so well expressed, go far toward explain- 

 ing the relation that the science of biology bears to the 

 science of geology, for it clearly shows that 

 it is chiefly through the interdependent bi- 

 ologic science of palaeontology. At the dawn 

 of life the earliest organisms were of forms most simple, 

 and from them grew a mighty tree with myriads of 

 branches, limbs and twigs, and as these became differen- 

 tiated during enormous stretches of time they produced, 

 in the majority of cases, groups of organisms which were 

 more and more specialized and complex in structure. So 

 that during the almost inconceivable lapse of time repre- 

 senting earth's physical history, branches of this great 

 tree have gradually produced such remarkably specialized 

 groups of beings, as modern teleostean fishes, modern 

 reptiles, modern birds, modern mammals, and, as a fam- 

 ily of the latter, modern men. 



The terminal twiglets of this vast organic growth and 



