AND THE PROBLEM OF DIASTATAXY. 325 
What obtains amongst the Pigeons Dr. Chalmers Mitchell has 
more recently shown (5) obtains also among the Kingfishers. 
Moreover, in this group the conversion of the diasta- into the 
eutaxial wing is still more clearly shown. Amongst different 
species of the same genus, some are diasta-, some eutaxic. Ceryle 
maxima, for instance, is diastataxic, and retains all the coverts 
of the displaced remex ; but Ceryle irula and C. americana are 
eutaxic, having eliminated the whole of the tell-tale transverse 
row of coverts. By the same process Halcyon rut'a has also 
become eutaxic. If evidence be needed that this interpretation 
is correct, it may be obtained from the wing of Halcyon jrileata, 
inasmuch as the last stages in the evolution of the eutaxial 
wing are here traceable in the three small feathers belonging to 
the minor coverts, which are all that now remain of the fifth 
transverse row. Hitherto no such completely transitional stages 
have been available. Their discovery is of great importance, since 
the presence of eutaxic wings in what may be described as 
diastataxic groups has long been a stumbling-block. 
The question now very naturally arises: Which are we to 
regard as the more primitive arrangement, the diasta- or the 
eu-taxic 1 That one is a modification of the other there can be 
no doubt. Adopting the terms recently coined by Dr. Mitchell, 
I contend that the eutaxic is to be regarded as the archccentric 
condition, and that the diastataxic is a uniradial apocentricity 
thereof, which probably made its appearance at a very early period 
in the phylogeny of the class Aves, and possibly, together with 
the segmentation of the pterygoid, and the consequent changes 
in the arrangement of the palatine bones, to which I have lately 
drawn attention (11). If this be so, then we must regard the 
whole of the Neoguathre (Carinatae) as diastataxic forms, many 
of which have once more become eutaxic, whilst others are in 
process of becoming so. 
I base these conclusions largely, but not entirely, on the evidence 
obtainable from a study of the wings of embryos, feeling convinced 
that what appears during the ontogeny represents the phylogenetic 
history of the wing. That the embryological record may be 
falsified we all know ; but crenogenetic changes are generally 
traceable to adaptation to the needs of the developing organism, 
VOL. vi i. 
Y 
