COMPARATIVE ANATOMY AND GENERAL BIOLOGY 335 



the cause of the form. Conclusions from this method must usually 

 be presumptive. Hence we must wherever possible call experi- 

 mentation to our aid, for this is preeminently the method that 

 yields evidence direct and immediate. But here again we must 

 recognize limitations. Undoubtedly there is a wide range of form 

 and structure that lies wholly beyond the reach of direct experi- 

 mentation. How, for example, can we hope to touch, except per- 

 haps indirectly and from afar, such a problem as that of the phylo- 

 geny of mammalian teeth? It is quite possible that experiments 

 on the developing teeth might be made, as, for example, by depriv- 

 ing the emb^o of salts necessary to tooth substance; or by arti- 

 ficially altering the pressure on the incipient teeth in some of the 

 marsupials whose embryonic life is largely extra-uterine. But with 

 all the necessary complexities of manipulation, and with the wide 

 scope of inference that would be necessary to determine the bear- 

 ings of the results of such experiments, I do not see that this method 

 can be expected to yield results for the problem as trustworthy as 

 those that may be looked for from comparative embryology. And 

 the same thing must, it seems, be true of very many problems 

 presented by the higher animals especially. 



I should like, did time permit, to say something on the part 

 comparative anatomy must play in the, to me, wonderfully enticing 

 field of animal ecology. But I must forbear. 



I may state the essence of this paper thus: From the point of 

 view of its problems rather than of its materials and methods of 

 research, the great biological field is indeed one. Its essential unity 

 can be realized and preserved, and these problems most effectually 

 worked at, by drawing the lines of specialization around problems 

 rather than around masses of facts. By this procedure we should 

 be led to appraise more justly methods and facts, and should be 

 compelled to see the necessity of employing any and all of these 

 that might help us on our way. Comparative anatomy ever has 

 held, and ever must hold, both for its methods and its substance, a 

 place of foremost importance in biological research. It, along with 

 embryology, which indeed it must include so far as concerns later 

 stages of development, is one of the surest passports of training to 

 the biological point of view. 



It is of primary importance in furnishing and applying criteria 

 of the value of evidence in problems of affinity, of phylogeny, and 

 hence of classification. 



It is, in both its methods and substance, of great importance to 

 Developmental Mechanics. 



