Chap. I.] EVOLUTION. 13 



" The history of the individual is a compressed epitome 

 of the history of the race." 



Those, therefore, who desire to obtain a complete 

 knowledge of animals or, indeed, of any one animal, 

 must not be contented with an account of the anatomy 

 of the adult ; they must direct their attention also 

 to its development, and become the students of 

 Embryology, while they must no less take care to 

 study the history of the animal, or of its allies, in the 

 past ages of the world, or to know something of its 

 Palaeontology. 



These two branches, Embryology and Palaeont- 

 ology, are of the greatest assistance in an endeavour 

 to obtain some clear idea of the morphology of animals ; 

 but a weapon no less sure and no less important is that 

 of comparison, by means of which similar parts in 

 different organisms are studied and explained ; no 

 better aid to safe j udgment can be afforded, and it must 

 be used unceasingly and unsparingly. 



EVOLUTION. 



The great maze and mass of facts which are found 



O 



in works on zoology or comparative anatomy are 

 hardly to be held together without the bond of phi- 

 losophy ; the grouping of facts, and, still more, the 

 grouping of animals, must be always more or less un- 

 intelligent, mechanical, and artificial, unless we make 

 some use of some kind of explanation. That which 

 we shall use here will be founded on the belief that 

 there is a blood relationship, or relationship by descent 

 and inheritance, between every member of the animal 

 kingdom; and that, were it possible to know all the 

 facts, we could make a genealogical tree for animals, 

 which should be as exact and definite as the family 

 tree which is drawn up by the genealogist or the 

 herald. That division of biology which busies itself 

 with genealogical problems is known as Phylogeiiy. 



