RELATIONS OF ANIMAL MORPHOLOGY 249 



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 append- 

 ages of the nudibranch mollusk Eolis are derived from material split 

 off in a regular manner and at regular intervals from a group of cells 

 lying in the tail-end of the developing animal. * Thus the interpreta- 

 tion 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 indis- 

 pensable to morphology is in the light it has thrown on homology. 

 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 regardless of function or even 

 ultimate anatomical 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 evo- 

 lution. When, however, twenty-two vertebrae in place of twenty- 

 one can nonplus the seeker after homology, its ethereal nature is 

 sufficiently indicated. 2 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 evolution. 



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 charac- 

 teristics are, on the whole, such as enable the animal to thrive in 

 its environment. We are struck by their "adaptive" nature. 



I am well aware that twenty years or so ago this side of morpho- 

 logy the side, namely, of the accounting for an organism's form 

 on the ground of use was little cultivated. 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 farther 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 natural inquiry as to use was stifled. Some one said that 

 function varies while the form persists. 3 This phrase became a 

 dogma, and function was considered a matter too trivial for con- 

 sideration. Homology was the study for men of science; analogy 

 was for the dilettanti. Morphologists should have been warned by 

 cases like the whale, whose teeth cannot be homologized with those 



1 C. B. Davenport, Studies in Morphogenesis, i, On the Development of the Cerata 

 in asolis, Bulletin of the Museum of Comparative Zoology, Harvard College, xxiv, 

 141-148, 1893. 



2 See W. Batesoix, Materials for the Study of Variation, 28-33 (1894) . 

 1 Sometimes called "Dohrn's Law." 



