CUSP RECTIGRADATIONS 



229 



i 



the independent evolution of identical structures in the teeth of 

 different families of mammals, especially in relation to the homologous 

 " antecrochet " and "crochet' folds in the teeth of horses, rhinoceroses, 

 and we may now add, of titanotheres (Oshorn, '94, p. i^OS . In tin- 

 present communication I propose to treat somewhat more fully of 

 the same phenomenon, as a special form of hoinology which has heen 

 clearly defined hy Lankester in 1874 as homoplasy, hut into which 

 paleontology has brought the idea of " potential." 



TlFK P.IJOAD SlGXlFK'ANCK OF ANAF.QCY. 



We are familiar with the classic distinction of analogous organs 

 as having a similarity of function: ancdoyy (Owen, '43, p. 374), "a 

 part or organ in one animal which has the same function as another 

 part or organ in a different animal"; 

 Lankester ('70): "Any two organs 

 having the same function are analogous, 

 whether closely resembling each other 

 in their structure and relation to 

 other parts or not : and it is well 

 to retain the word in that wide 

 sense." Analogous organs may or 

 may not be homologous. " Analogy ' 

 is therefore an extremely broad and 

 comprehensive term, and it appears 

 that we must include under it all 

 cases of the similar evolution of organs 

 either of common or of different origin 

 due to similarity of function. For 

 exam} tie, the " analogous variation " 

 of Darwin, the " homoplasy ' of Flf , . m Fourth upper premolar and first 



1 flnlcpsjfpv ill rnvf- it lpat flia "nnn molar of primitive ungulates. A, Ev.protogo;>i<i. ; 

 111 part at least, me B> Hln . a< . other i UM . y t believed to be geneti- 



vpro-piw " of fipvniflii wvitprQ rlip call - v related, J'et exhibiting independent i.r 



W1 homoplastic evolution of homologous cusps. 



" homomorphy ' of Furbringer, the 



" heterology," "parallels," and "parallelism" of Hyatt, of Cope ('68, 

 also Origin of the Fittest, p. 96), of Scott, and of most American 

 writers, are all illustrations of analogy and may Vie very misleading 

 as to hoinology. 



As Scott observed in 1896, "Parallelism 1 and 



convergence 



of 



J The term "parallelism'' was employed by Cope in his essay of 1868 on the "Origin 

 of Genera" (reprinted in the Origin of the Fittest) in two quite different senses: first, 

 in relation to recapitulation in ontogeny, "Those which accomplish less [stages] are 

 parallel with the young of those which accomplish more [stages] " ; second, quite in the 

 modern sense (op. cit., pp. 96-104) of independently acquired resemblances in different 



