700 



SCIENCE. 



[N. S. Vol. XX. No. 517. 



adult form depends on a knowledge of its 

 development. 'In terms of the ancient 

 riddle,' says Bateson {Nature, Vol. 70, p. 

 412) in his recent address as president of 

 the section of zoology in the British Asso- 

 ciation, 'In terms of the ancient riddle 

 we must reply that the owl's egg existed 

 before the owl, and if we hesitate about 

 the owl we may be sure about the bantam. ' 

 The characteristics of the adult form are 

 implicit in the fertilized egg and are de- 

 termined by the Anlagen of the character- 

 istics wrapped up in that egg. We know 

 now that upon the symmetry of the egg 

 and of the successive cleavages often, if 

 not typically, the symmetry of the adult 

 form depends, and that upon the lack of 

 symmetry of cleavage in Gastropods their 

 lack of symmetry is probably to be re- 

 ferred. In the successive cleavages defi- 

 nite organ-tracts are marked off and still 

 later the epidermal organs, such as hair, 

 feathers and scales — the bearers of the 

 ipore evident heredity characteristics— are 

 laid down in regular lines radiating often 

 from single points or groups of cells, thus 

 simplifying the problem of inheritance of 

 peculiarities of plumage or coat color 

 by referring them back to transmission 

 through particular cells or cell groups. It 

 has thus been possible to show that all 

 the numerous dorsal appendages of the 

 nudibranch mollu.sc Eolis are derived' from 

 material split off in a regular manner and 

 at regular intervals trom a group of cells 

 lying in the tail end of the developing 

 animal. Thus the interpretation of the 

 mechanism of transmission of qualities is 

 first gained from a study of embryology. 

 A second way in which embryology has 

 been regarded as indispensable to morphol- 

 ogy is in the light it has thrown on homol- 

 ogy. By homology— the will-o'-the-wisp 

 of morphology — is meant such a similarity 

 of unlike things in different species as 

 would justify their receiving the same 



name. And one of the strongest grounds 

 of a homology is similarity of origin re- 

 gardless of function or even ultimate an- 

 atomical connections. The search for 

 homologies has led to the idealization of 

 the 'type,' and this more than anything 

 else has blinded morphologists to the facts 

 of variation and evolution. When, how- 

 ever, twenty-two vertebrte in place of 

 twenty-one can nonplus the seeker after 

 homology, its ethereal nature is sufficiently 

 indicated. Homology may, indeed, exist 

 between normal types, but the abnormal 

 or pathological is often beyond homology 

 and yet just the abnormal is, paradoxical 

 as it may sound, the important for evolu- 

 tion. 



As we study an organism's form we see 

 that it is not made up merely of a great 

 number of characteristics, but that these 

 characteristics are, on the whole, such as 

 enable the animal to thrive in its environ- 

 ment. We are struck by their 'adaptive' 

 nature. 



I am well aware that twenty years or so 

 ago this side of morphology— the side, 

 namely, of the accounting of an organism's 

 form on the ground of use— was little cul- 

 tivated. Morphology had for its aim the 

 discovery of the interrelation of parts in 

 the individual organism and the homology 

 of parts in different individuals or species, 

 and if it sought to go further it indulged 

 only in speculative inferences as to the 

 probable function of the parts. On the 

 whole the student's attention was directed 

 towards connections of organs and his nat- 

 ural inquiry as to use was stifled. Some 

 one said that function varies while the 

 form persists. This phrase became a dog- 

 ma and function was considered a matter 

 too trivial for consideration. Homology 

 was the study for men of science ; analogy 

 was for the dilettanti. Morphologists 

 should have been Avarned by cases like the 

 whale whose teeth can not be homologized 



