248 THE GENESIS OF SPECIES. [CHAP. 



portance, all point to such a mode of specific manifesta- 

 tion. 



One very good example has been adduced by Prof. 

 Flower in the introductory lecture of his first Hunterian 

 Course. 6 It is the reduction in size, to a greater or less 

 degree, of the second and third digits of the foot in Aus- 

 tralian marsupials, and this, in spite of the very different 

 form and function of the foot in different groups of those 

 animals. 



A similarly significant evidence of relationship is af- 

 forded by processes of the zygomatic region of the skull in 

 certain edentates existing and extinct. 



Again, the relation between existing and recent faunas 

 of the different regions of the world, and the predominating 

 (though by no means exclusive) march of organization, from 

 the more general to the more special point in the same 

 direction. 



Almost all the facts brought forward by the patient 

 industry of Mr. Darwin in support of his theory of " Natu- 

 ral Selection," are of course available as evidence in favor of 

 the agency of preexisting and similar animals in specific 

 evolution. 



Now. the new forms must be produced by changes tak- 

 ing place in organisms in, after, or before their birth, either 

 in their embryonic, or toward or in their adult, condition. 



Examples of strange births are sufficiently common, and 

 they may arise either from direct embryonic modifications 

 or apparently from some obscure change in the parental 

 action. To the former category belong the hosts of in- 

 stances of malformation through arrest of development, and 

 perhaps generally monstrosities of some sort are the result 

 of such affections of the embryo. To the second category 

 belong all cases of hybridism, of cross-breed, and in all prob- 



6 Introductory Lecture of February 14, 1870, pp. 24-30, Figs. 1-4. 

 (Churchill & Sons.) 



