rrsp KK(TH:i:.\i)ATKxs 



described and do describe two kinds of agreement, the one, now proposed to 

 be called "homogeny," depending simply on the inheritance of a common part; 

 the other, proposed to be called " homoplasy," depending on a common action of 

 evoking causes or moulding environment on such homogenous parts, or on parts 

 which for other reasons offer a likeness of material to begin with. 



Homologv thus includes - 



[ Homogeny. 



It follows that subsequent writers, including myself, have misused 

 the term "homoplasy," confusing it with " parallelism " and "con- 

 vergence," which, as we have seen, may affect absolutely non-homologous 

 structures. Homoplasy should be confined to structures in which there 

 is an element of homology. 



Independently of Lankester (that is, not familiar with his paper) 

 I had therefore reached a similar conclusion thiough years of observation 

 in paleontology. I would now like to expand an idea which he also 

 lightly suggested in 1870 in the words, "or on parts which for other 

 reasons show a likeness of material to begin with!' 



THE LAW OF HOMOPLASY AS ix PART IDENTICAL WITH DEFINITE 



OK DETERMINATE VARIATION. 



As observed in the evolution of the teeth especially, homoplasy 

 appears to be of very great importance, not on the technical grounds 

 of uniformity in nomenclature, but because it seems to coincide with 

 the principle of definite or determinate evolution, a principle which 



me. 



or. 



me. 



pa. 



pr. 



Fin. -J13. Superior molars of primates, Anaptomorphus to Homo, showing independent or 

 homoplastic origin of the hypocone, hv, from the cinguliiin. 



may be of wider application. 1 From the time of the " < higin of 

 Species" it has been admitted that evolution, so far as it depends 

 upon variation, is not in every possible direction, but is limited to 

 certain changes, the expression of certain hereditary or constitutional 

 causes which we do not in the least understand. The evolution of 

 the teeth of mammals enabled me in 1889 to give many concrete 



1 See especially the correspondence of Darwin and Asa Gray ; also Osborn, The 

 Palfeontological Evidence for the Transmission of Acquired Characters, Xafiire, Jan. 9, 

 1890; the Orthogenesis and Orthoplasy of Kimer, Lloyd Morgan and Baldwin; Baldwin's 

 Dictionary of Philosophy and Pxyclioloyy, Vol. I., p. '243. 



