6o Southern Cross. 



he confesses that "the present system of homology must probably 

 be retained as a basis of notation, imperfect though it is, and 

 although it is founded on a misconception of essential facts." 



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

 Mr. Bateson's arguments. He has certainly indicated the difficulties 

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

 bility. 



As a critic of Mr. Bateson, Dr. Kiikenthal acknowledges the 

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

 term) reduplication in teeth, and believes that such reduplication or 

 splitting may in certain cases occur in any cheek-tooth. But, since 

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

 nothing to prevent the reading of the homologies. Thus in the case 

 of skull No. 3245, 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 regarding each of the remainder, starting from the last two, as 

 homologous — a supposition which is, indeed, not denied by Mr. 

 Bateson. 



Continuing, Dr. 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 

 increase in number and the formation of a new species possessing 

 six cheek-teetli. 



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

 less frequent will be intermediates, and the more difficult, although 

 not impossible, will it be to follow the phylogeny. Even were the 

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

 forms predominant, there would still occasionally occur five-toothed 

 individuals to indicate the origin of the former. Difficulties in 

 reading homologies might increase ; impossibility would not exist. 



Turning to another form of variation in Mammalian teeth, the 

 appearance of extra teeth, as in Halichmrus,^ in which the upper 

 jaw may possess six instead of live cheek-teeth. Dr. Kiikenthal 

 remarks that in this case the new teeth are always at the same place 

 at the posterior end of the jaw. They are not the result of redupli- 

 cation, but represent an entirely new factor. Here again homology 

 is still possible and even easy, the five teeth of a typical skull corre- 

 sponding to the first five of a six-toothed skull, and the sixth tooth 

 of the latter being something new. 



^ See A. Nehriug, Ueber Gebiss uiul Skellett von Halichtrus grypus. Zool, 

 Anzeiger, p. 610, 1873. 



