142 THE INDUCTIONS OF BIOLOGY. 



ology comes next in order. Yon Baer found that in its 

 earliest stage, every organism has the greatest number of 

 characters in common with all other organisms in their 

 earliest stages ; that at a stage somewhat later, its structure 

 is like the structures displayed at corresponding phases by a 

 less extensive multitude of organisms ; that at each sub- 

 sequent stage, traits are acquired which successively distin 

 guish the developing embryo from groups of embryos that it 

 previously resembled — thus step by step diminishing the 

 group of embryos wmich it still resembles ; and that thus the 

 class of similar forms, is finally narrowed to the species of 

 which it is a member. This abstract proposition will per- 

 haps not be fully realized by the general reader. It will be 

 best to re-state it in a concrete shape. The germ 



out of which a human being is evolved, differs in no visible 

 respect from the germ out of which every animal and plant is 

 evolved. The first conspicuous structural change undergone 

 by this human germ, is one characterizing the germs of 

 animals only — differentiates them from the germs of plants. 

 The next distinction established, is a distinction exhibited by 

 all Vertebrata; but never exhibited by A?innlosa, Mollusca, or 

 Cwlenterata. Instead of continuing to resemble, as it now 

 dGes, the rudiments of all fishes, reptiles, birds, and mammals ; 

 this rudiment of a man, assumes a structure that is seen only 

 in the rudiments of mammals. Later, the embryo undergoes 

 changes which exclude it from the group of implacental 

 mammals ; and prove that it belongs to the group of placental 

 mammals. Later still, it grows unlike the embryos of those 

 placental mammals distinguished as ungulate or hoofed ; and 

 continues to resemble only the unguiculate or clawed. By 

 and by, it ceases to be like any foetuses but those of the quad- 

 rumana ; and eventually the foetuses of only the higher 

 quadrumana are simulated. Lastly, at birth, the infant, 

 belonging to whichever human race it may do, is structurally 

 very much like the infants of all other human races; and 

 only afterwards acquires those various minor peculiarities of 



