Vol. XXII. 



CA.MI'P.ELL, A. G., Acauthicac or ThonihUls. 197 



D. — vSi'oKT OK Casuai, Variation. 



Independent of A, B, and C, which are ordinary common types 

 of variation, there is this sportive variation not arising from any 

 obvious natural reason, and often right across the track of 

 ordinary variation. I refer to such variation as a red rose 

 appearing casually upon a white-t^ovvered bush ; many similar 

 cases in the animal world can be called to mind. Whether this 

 is a throwing back, or variation due to the appearance of char- 

 acters belonging to some distant progenitor, or whether it is 

 entirely casual and without reason, is a question with which we 

 are not now concerned. But it is affirmed that this kind of 

 variation is not sufficiently taken into account when dealing with 

 the distribution of birds. I believe that Acanthiza ewingi, for 

 instance, of Tasmania, is a sport, and proof will be offered in 

 the notes dealing with that species. 



* * * * 



To further illustrate : Geobasilcus chrysorrhous has yellow 

 upper tail-coverts. G. uropygialis has coverts and base of tail 

 tawny. G. regidoides exhibits a colour (buff) which may be said 

 to lie between these two extremes. 



Can we honestly consider this a link, or intergradation, and 

 say that all three must be lumped into one species? The idea is 

 absurd. Though they may not show much difference otherwise, 

 yet the contrast in colour between yellow, bufif and tawny is 

 obviously distinct and specific. 



Again, Geobasiletis squamaiiis, from North Queensland, has 

 upper tail-coverts yellow, like G. chrysorrhous, and base of tail 

 bufif like G. reyiiloides. Is this an intergradation? \Ve are nar- 

 rowing down to finer points, but when we see that squamatus 

 has under surface citron yellow, which neither of the others has, 

 its specific difference is maintained. 



Take another example, A. pusilla and A. pyrrhopygia (Gould). 

 The former may be termed the coastal species of browner mantle 

 and duller rump, the latter the interior species of greyer mantle 

 and brighter rump. Is A. apicalis of W.A. a link between the 

 two, with its brown mantle and bright rump? To casual ob- 

 servers all three may seem alike, but close examination is re- 

 quired to bring out the facts. Since Gould's day mv'ch material 

 has been procured across the whole width of Australia. Many 

 interior, far interior and desert races have been brought to light. 

 I confidently assert that these three species stand distinct and 

 separate, as do the Geobasilcus already referred to, but proof is 

 too lengthy to be offered here. 



W'hat constitutes reasonable sub-specific difference may be 

 illustrated with Geobasileus chrysorrhous, a very common bird, 

 whose range extends over nearly the whole continent. Taking 

 the colour of the under tail-coverts as a guide, we find yellow, 

 buff, or white. This is a small feature, but not unimportant. 

 Yellow under-coverts are found in birds of the northern half of 



