MancJiester Memoirs, Vol. I. (1906), No. 3. 87 



tion,' though it is not a recapitulation of any adult 

 ancestral type, but merely a repetition of similar onto- 

 genetic functions by cells which have inherited a similar 

 structure.*^' In destiny, however, such cells may be 

 exceedingly diverse : ' Furchungsmosaik,' as Driesch has 

 it, 'braucht kein Mosaik der Potenzen zu sein." It is 

 only within comparatively narrow limits that origin and 

 destiny can coincide. 



Nor is the failure of embryology to provide an in- 

 fallible criterion of homology evident in the history of 

 the germ-layers alone. In organogeny we are often 

 reduced to an exactly similar impasse; the oviduct of 

 the Elasmobranchs, to take an example, bears the closest 

 resemblance anatomically to the same organ in the air- 

 breathing Vertebrates ; and yet devclopmentally it is 

 totally dissimilar, arising from the pronephric half of the 

 segmental duct, while in the other forms it has nothing 

 to do with any part of the excretory system. Morpholo- 

 gists, as a matter of fact, adopt the embryological evidence 

 when it suits them and ignore it when the facts are 

 inconvenient. In discussing that vexata qucestio the 

 homology of the ear-bones, for instance, Gegenbaur,™ 

 while unhesitatingly accepting the equivalence, as based on 

 development, of the Mammalian stapes with the Saurop- 

 sidan columella and of both with the hyomandibular of 

 Fishes, just as unhesitatingly passes over as a caenogenetic 

 modification the origin of the Amphibian columella from 

 the auditory capsule. 



This, of course, is the usual apology offered ; it is the 

 one which Haeckel himself suggested to meet difficulties 



^* Such a repetition as that here indicated is what I understand O. 

 Hertwig to mean by his ' Modifikation des biogenetischen Grundgesetzes ' 

 " Handbuch der Entwicklungslehre der Wirbelthiere." Einleitung, p. 56, 57, 

 Jena, 1901. 



7 " Vergleichende Anatomic der Wirbelthiere," vol. i, p. 440, S96 sqq. 

 Leipzig, 1898. 



