Mainiiialia. 59 



following tlie individual history of each tooth is notorious. Espe- 

 cially is this the case because "though variation may sometimes 

 respect the individual homologies, yet this is by no means a universal 

 rule ; and, as a matter of fact, in all cases of Multiple Parts, as to 

 the variation of which any considerable body of evidence has been 

 collected, there are numerous instances of new forms arising in 

 which what may be called the stereotyped or traditional individuality 

 of the members has been superseded." 



Judged by the ordinary rules of morphological criticism, this 

 [original] specimen [of Ommatophoca rossii\ shows one or both of two 

 things : — 



(1) The first premolar of Onimatoylioca may in itself represent 

 two premolars of an ancestor ; 



Or (2) in the descendants of Oinmatoplioca- the single first 

 premolar 7nay be represented by two distinct and separated pre- 

 molars. 



One or both of these propositions may be true. If the division 

 of the other three first premolars were as complete as that of the left 



p.m. — , there would be no indication of their origin. But if it is 



possible for a premolar to represent or to be represented by two 

 premolars, without any visible indication of its double nature, may 

 not the same be true of the premolars of other forms ? may it not be 

 true of teeth generally ? And if it is true, how are the homologies 

 of teeth to be determined ? 



Mr. Bateson's arguments carrv with them all the virtues and 

 vices of brilliant destructive criticism. He has seized a tempting 

 opportunity to attempt the downfall of, or at least to heap discredit 

 upon, the theory of homology, a theory which, like all other human 

 theories, is but a working hypothesis, and as such no more unsatis- 

 factory or satisfactory than others of its kind. Without the theory 

 of homology, much of the l)est biological work of the past century 

 would be barren and meaningless. Eegarded by its light, a good 

 deal of it seems to tend towards tlie same goal. To brand our 

 system as " imperfect " is to tell us what we already knew. To 

 discredit that system is to retard rather than to advance knowledge 

 — unless the objector can produce another system better and more 

 workable in its stead. 



This Mr. Bateson, like many other destructive critics, con- 

 spicuously fails to do. In fact he does not e^'en attempt a task 

 which he probably regards as impossible. The weakness of his 

 position is best demonstrated by his concluding paragraph, wherein 



