IO2 Darwin, and after Darwin. 



similar processes of development in the life-histories 

 of their respective species in so far, I mean, as the 

 two sets of changes admit of being proved parallel. 



In the only illustration hitherto adduced viz. that 

 of deers' horns the series of changes from a one- 

 pronged horn to a fully developed arborescent antler, 

 is a series which takes place during the adult life of 

 the animal ; for it is only when the breeding age 

 has been attained that horns are required to appear. 

 But seeing that every animal passes through most of 

 the phases of its development, not only before the 

 breeding age has been attained, but even before the 

 time of its own birth, clearly the largest field for 

 the study of individual development is furnished by 

 embryology. For instance, there is a salamander 

 which differs from most other salamanders in being 

 exclusively terrestrial in its habits. Now, the young 

 of this salamander before their birth are found to 

 be furnished with gills, which, however, they are never 

 destined to use. Yet these gills are so perfectly 

 formed, that if the young salamanders be removed 

 from the body of their mother shortly before birth, 

 and be then immediately placed in water, the 

 little animals show themselves quite capable of 

 aquatic respiration, and will merrily swim about in 

 a medium which would quickly drown their own 

 parent. Here, then, we have both morphological and 

 physiological evidence pointing to the possession of 

 gills by the ancestors of the land salamander. 



It would be easy to devote the whole of the present 

 chapter to an enumeration of special instances of the 

 kinds thus chosen for purposes of illustration ; but 

 as it is desirable to take a deeper, and therefore 



