GENERAL PRINCIPLES OF MORPHOGENESIS 115 



It has been pointed out by von Bonin ('45) that the logical founda- 

 tions of the concept of morphology based on phylogenesis as devel- 

 oped by T. H. Huxley, Gegenbaur, and others of their time are in- 

 secure. The mathematical argument need not here be examined, for 

 it is based on certain restricted postulates, and in animal evolution 

 there are many variables not embraced by these postulates. It cer- 

 tainly does not follow that "the task of understanding structures on 

 the basis of their phylogenetic history" is "an insoluble problem." 

 Though neither cultural history nor phylogenetic history has been 

 reduced to mathematical formulation, there is general agreement 

 that history, judiciously interpreted, is an accredited guide for under- 

 standing the present and prognosticating the future. Phylogenetic 

 history is not a sealed book, and Dr. von Bonin assures me that he 

 would be the last to deny a positive value to the historical approach 

 to problems of morphogenesis and that such studies have actually 

 contributed much toward an understanding of human cerebral struc- 

 ture and function. The positive paleontological evidence regarding 

 the phylogeny of the brain is more extensive and illuminating than 

 is generally recognized. Though fossilized brains are unknown, the 

 very large number of casts of skull cavities, when skilfully inter- 

 preted, yield a surprising amount of reliable information about the 

 nervous organs which once occupied those cavities, as illustrated, for 

 instance, by Stensio's studies ('27) of fossil ostracoderms. It must be 

 freely granted, of course, that conclusions reached are tentative, to 

 be accepted only as checked against other lines of evidence, particu- 

 larly the known sequence of evolutionary history as revealed by fos- 

 silized skeletal remains. 



No single mode of attack upon problems of morphogenesis is ade- 

 quate. Experimental methods yield the most decisive evidence, and 

 these require adequate knowledge of anatomical structure. This last 

 is the contribution of comparative anatomy and comparative em- 

 bryology, and both of these must be functionally interpreted to be 

 fruitful. The anatomist should recognize the limitations of his meth- 

 od. His task is to lay foundations — stable and adequately broad — 

 and to suggest fruitful working hypotheses. The Amphibia occupy a 

 strategic position here for the same reason that the experimentalists 

 find them so useful. 



