i8 95 . 



NOTES AND COMMENTS. 221 



the successive stages follow upon one another that it is sometimes 

 extremely difficult to arrange them all in order and to distinguish 

 clearly those members which belong in the main line of descent, and 

 those which represent incipient side branches. Some phylogenies 

 actually suffer from an embarrassment of riches.'' 



Continuity in a series of descent is not peculiar to mammals. 

 Waagen, years ago, found it in Ammonites ; other observers in other 

 groups, and we agree with Professor Scott when he says that it 

 occurs " wherever the phyla can be worked out in detail." 



Similarly, Professor Scott finds a great contrast between the 

 results obtained by Mr. Bateson from his study of variations in 

 meristic series, and the changes in meristic series as recorded in 

 palaeontology. For the details of the evidence we must refer readers 

 to Professor Scott's paper, as indeed the whole object of this note is 

 to call attention to the paper. It is shown from a consideration of 

 teeth and of digits that there is a marked discrepancy between 

 individual and phyletic variation. In the latter there is a marked 

 individuality in the elements of the series, an individuality retained 

 all through the successive changes. However a single member of the 

 series may be modified, it can still be identified with certainty. 

 Moreover, new members are not introduced irregularly and casually. 

 The series show a gradual and steady reduction in number, and there 

 is a definite correspondence, though not always identity, in the 

 reductions of parallel series. 



Professor Scott suggests that the difficulties of such discordance 

 in the evidence drawn from phylogeny and from individual abnor- 

 malities may lie in the assumption that individual variations are, or 

 may be, incipient species. Following Waagen and Neumayr, he dis- 

 tinguishes these individual abnormalities from the slow modifications 

 recorded in palaeontology, and calls the former variations, the latter, 

 mutations. " It may," he says, " be the outcome of future investiga- 

 tion that, while variations are due to the union of changing hereditary 

 tendencies, mutations are the effect of dynamical agencies acting long 

 in a uniform way and the results controlled by Natural Selection." 



The Classification of Birds. 



Perhaps no group in the animal kingdom offers more difficulties 

 and more attractions to the biologist who is interested in the problem 

 of species. The structure of all birds is very closely alike. Those 

 accustomed to the anatomy of most other groups would be astonished 

 at the apparently small differences in structure upon which the 

 taxonomist is compelled to rely. The number of species and genera 

 is enormous, the amount of work done upon the group by field 

 naturalists, museum naturalists, and by anatomists is monumental. 

 All classifications are profoundly unsatisfactory even to their inventors. 



