1918.] Rejections by Birds of Eggs unlike their own. 127 



deeper blue shade, and is even seen in this aberrant genus 

 as a yellow-green patch. As the immature of the genus 

 Purpureicephalus shows the evolution of the mature from a 

 green bird, we have here a case of a structural difference 

 developing at a more rapid rate than a colour-change. We 

 are compelled to indicate our lack of knowledge of how 

 colour-changes and structural changes are produced, but we 

 do know that study of colour and colour-pattern will prove 

 even more valuable than study of structural differences. 



EXPLANATION OF PLATE III. 



The upper and under sides of tlie following Parrots : — 



1. Platycercus caledo7iicus, 



2. „ eleyans. 



3. „ Jlaveolus. 



4. „ adscitus. 



5. ,, e.vimius. 



6. Purpureicephalus spurius. 



7. Platycercus icterotis. 



8. „ venuxtus. 



9. Barnardius zonarkis. 



VII. — Rejections by Birds of Eggs unlike their oivn : with 

 Remarks on some of the Cuckoo P^'oblems. By C. F. M. 



SWYNNERTON, C.M.B.O.U. 



I HAVE referred very briefly to the general result of my 

 first season^s experiments in the above connection in 

 'The Ibis' for October 1916 (p. 557). I returned to the 

 attack last year, partly to ascertain whether really fine 

 discrimination is ever shown. The experiments were in- 

 terrupted while still incomplete^ but Major Meiklejohn's 

 interesting and comprehensive paper in the April 'Ibis,' 

 just received, recalls me to the subject and suggests the 

 publication of my summary of them. .Except in the case 

 of the first dozen experiments, I only recorded the details of 

 such as struck me as being of somewhat special interest ; 

 but not less^ I should say, than fifty were carried out in all 



