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them with an appearance of dogmatism, but I clearly understand that 
they are governed in every case by the above limitation. My excuse 
for making them is that the phyletic relations of birds have always 
presented a very difficult problem, and that none of the customary 
means has produced a satisfactory solution. So when I find that bird 
parasites, owing to their peculiar biological condition, seem to shed 
some light upon this problem, I think it worth while to put these 
indications on record. The morphologist can confirm or refute them 
at his leisure. * 
With this much explanation I proceed to the final question—Is Apteryx 
a rail? If not, how does it come to possess ralline parasites? The 
mature opinion of Prof. Kellogg, after twenty years’ study of Mallophaga, 
is that “the host distribution of these wingless permanent ectoparasites 
is governed more by the genetic relationships of the hosts than by their 
geographic range, or by any other ecologic conditions” (1914, p. 259). 
That opinion is based on—“The fact, proved by abundant cases, that 
two host species of wholly distinct geographic range and with no possible 
opportunity for contact such as would permit of the migration of 
wingless parasites from one to the other, may have, nevertheless, one 
or more parasitic species common to them both, is associated almost 
always with the further fact that these common hosts are closely 
related genetically.” Kellogg instances only the occurrence of the 
same parasitic species on two geographically segregated but phyletically 
connected hosts. In my paper (1914) published a month after Kellogg’s, 
but which had gone to press more than a month before it, I carry the 
hypothesis further; and apply it to the case of closely related parasitic 
species upon closely related hosts. And though I cannot lay claim to 
the same wide knowledge of Mallophagan species that Prof. Kellogg 
possesses, I had nevertheless been studying the group for some five 
years, purely from this point of view. Only one other explanation of 
the distribution of Mallophaga can be put forward, namely that it is 
due to convergence. I have not overlooked this possibility, but I do 
not find any evidence of this cause myself, and I do not think that the 
most ardent advocate of convergence, were he to look carefully into 
the actual conditions of Mallophagan distribution, would claim these 
conditions as the result of convergence. 
The only alternative is to believe that Apteryx and the rails are 
closely connected phyletically, unless one or other of the groups has 
acquired these particular parasites by some accidental transference. 
This supposition may be dismissed as far as the rails are concerned. 
7—2 
