Vol. xlii.J 98 



Other boxes show that amongst all Cuckoos wo occasionally 

 find eggs deposited in the nests o£ birds which can, under no 

 circumstances^ be considered in any way normal fosterers, 

 and these can only have been so deposited because there was 

 no nest of the proper fosterer available at the time the egg 

 was laid. 



Again, in some instances we see eggs deposited in the 

 nests of birds which could never have reared the young 

 Cuckoo, and in yet others the eggs are deposited in nests 

 from which the young could never have extricated themselves. 

 Amongst the latter may be mentioned that of Ahrornis in 

 hollow bamboos, and those of some of the Phylloscopi, which 

 breed in hollow trees with tiny entrances. 



But there is amongst the Cuculidffi an immense amount of 

 variation in the number of birds selected as foster-parents, 

 and wideness of selection is probably coincident with the 

 age of the form- of Cuckoo. In the oldest forms we shall find 

 the selection very much restricted and resemblance perfected, 

 in the intermediate genera and species the range of 

 fosterers wider and the resemblance between the eogs of 

 the foster-parent and those of the Cuckoo less advanced, and 

 in the most recent forms we shall find the greatest range of 

 selection and the least resemblance existing. This I propose 

 to enlarge on later on, in dealing with other points. Here 

 I would merely draw your attention to the fact that birds of 

 the Clamator group (Boxes Nos. 34 to 37) have very few 

 fosterers, and to these few they rigidly adhere ; birds of the 

 genus Hierococcyx (Boxes Nos. 2^0 to 30) have but few 

 normal fosterers, and to these they keep in some cases 

 rigidly, in others fairly regularly, the former when the 

 foster-parents are very common, the latter when the foster- 

 parents are less numerous. Thus IJ.varius practically never 

 places its eggs in any nests except those of Babblers of the 

 extremely common genera Argya and Turdoides, whilst 

 //. sparveroides generally places its brown egg in the nests 

 of Arachnotltera magna and JJrymochares nejjalensiSf which 

 are fairly common, only. 



