ORGANIC EVOLUTION 261 



processes of the making of the organisms of the present: 

 not armor nor bones nor any other finished parts of organs, 

 but the moulding processes of the basic materials out of 

 which all the organs are formed. In these processes embry- 

 ology gives us evanescent glimpses of the ground lines of 

 phylogeny in so far as they are preserved in the successive 

 stages of development of the individual. That many 

 features of all embryos are ancestral there can be no doubt. 

 It was the study of embryology that did most to compel 

 the acceptance of the doctrine of evolution in a past genera- 

 tion. And it was this also that stimulated to greater use 

 of the historical method in all fields of investigation. 

 Ontogeny has long been and will ever be one of the most 

 stimulating fields of biological investigation. It is the most 

 synthetic of all. In the bewildering array of forms, it finds 

 a few main types of development, themselves traceable to a 

 common type in the egg cell. And it shows, withal, how 

 little Nature creates : how much she merely transforms and 

 adapts. 



Study J4. The ontogeny of organs in the frog or salammider. 



Materials. The results of studies 25 to 28, together with 

 whatever additional available data reference works may 

 furnish, supplemented by whatever data may be at hand. 

 Ecker's Anatomy of the frog, and Holmes, The Frog, at 

 least should be available for reference. 



Tabulate all the organs that show marked ontogenetic 

 changes, under the following headings: 



I. Organs peculiar to developmental stages and wanting 

 in adult. 



II. Organs functional in young, vestigial in adult. 



III. Organs present in both, but serving a changed 

 function in adult. 



