6o SoiifJirrn Cross. 



he ronfoAses that "the jdosent system of homology must probably 

 lie rvtninwl as a basis of ni)tati(»n, imperfect though it is, and 

 nlthough it is fouiuletl on a misconception of essential facts." 



It is unnecessary, in the present connection, to deal further with 

 Mr. Ilateson's arguments. He has certainly indicated the difhculties 

 of nwling homologies ; he has not necessarily proved the impossi- 

 bility. 



As a critic of Mr. i'.ateson, Dr. Kiikenthal acknowledges the 

 pmbabK? existence of numerous instances of (to use Mr. Bateson's 

 term) mbiplication in teetli, and believes that such reduplication or 

 s)»litting may in certain ca.ses occur in any cheek-tooth. But, since 

 all intermediate stages of the phenomenon may be found, there is 

 nothing to jirevent the reading of the homologies. Thus in the ca.se 

 »>f skull No. ?y'l\h, he finds no difficulty in believing that at tlie 

 anterior end of the series two teeth on the left are homologous with 

 one on the right, and, that being so, there is nothing to prevent us 

 from n'gsirding each of the remainder, starting from the last two, as 

 homologous — a supi)osition which is, indeed, not denied by Mr. 

 Bnteson. 



Continuing, J)r. Kiikenthal thinks that, since in some cases each 

 of a pair of these reduplicated teeth may attain to the same size as 

 the remainder of the series, there may in this way arise a permanent 

 increa,st' in number and the formation of a new species possessing 

 six cheek-teeth. 



The more often the new six-toothed form alone occurs, the 

 le-Hs frequent will Ite intermediates, and the more difficult, although 

 not imj)o.s.sible, will it be to follow the phylogeny. Even were the 

 original five-toothed forms entirely ousted, and the new six-toothed 

 fonns predominant, thctre would still occasionally occur five-toothed 

 inclividuals to indicate the origin of the former. Difficulties in 

 rejiding lutmologius might increase; impossibility would not exist. 



Turning to another form of variation in Mammalian teeth, the 

 api»earance of extra teeth, as in Halichcerui^,^ in which the upper 

 jaw may pos.se8s six instead of \\\q cheek-teeth. Dr. Kiikenthal 

 n"niark» that in this case the new teeth are always at the same place 

 nl the jMisterior end of the jaw. They are not the result of redupli- 

 l)Ut re])resent an entirely new factor. Here again homology 

 .- -.ul |MMi.sible and even ca.sy, the five teeth of a typical skull corre- 

 »l».,ri,lifv. to the lirst five of a six-toothed skull, and the sixth tooth 

 "f >'r l)eing .something new. 



• S« A. Nfhriog, U.-bcr Oel.isR iiiid Skcllett vnii JI,tHch;rus m-inma. Zonl. 

 Anmger, p. fiio, 1873. ■ ' 



