AVIAN GENUS CHRYSOCOCCYX 39 



glossy cuckoos. These data, together with the facts presented else- 

 where in this report as to the degree to which host specificity has de- 

 veloped and the degree to which host-egg resemblance has become 

 marked, form the relatively meager body of information that we may 

 interpret as evincing evolutionary trends toward progressive hetero- 

 geneity in host fixation among the various species of the group. To 

 meet the need for convenient terms by which to express these variations 

 of host selection, I proposed the following. Alloxenia (with alloxenic 

 as its adjective) may be used to describe cases where each species of 

 parasite uses different host species; homoxenia (with homoxenic as its 

 adjective) may be used for those cases where two or more kinds of 

 parasites make use of the same host species (1937, p. 175). 



We are apt to think of Cuculus as having gone very far in adaptive 

 host-egg resemblance, but this is mainly because of the development of 

 host-specific ''gentes" in one species, Cuculus canorus. Certainly other 

 species of the genus do not show anything of comparable evolutionary 

 intensity, and it is to these less specialized parasites that the glossy 

 cuckoos may be compared. 



Thus, it appears that malayanus is to a large degree bound up in its 

 reproductive pattern with Gerygone warblers, and that osculans has 

 come to speciahze markedly on the speckled warbler, Chthonicola 

 sagittata (with the eggs of which its own have close similarity) and to 

 a lesser extent on the redthroat, Pyrrholaemus hrunneus (to the eggs 

 of which its own bear a fair but less precise resemblance). While it has 

 been claimed by Baker and others that the eggs of maculatus and of 

 xanhorhynchus indicate adaptive accommodation to sunbird hosts, 

 particularly Aethopyga and Arachnothera, these eggs are not as highly 

 peculiar in their coloration as are those of osculans, and therefore per- 

 mit one to think their speciaHzation may have been a matter of finding 

 hosts with fairly similar egg types rather than of developing an adap- 

 tive pattern in themselves. 



The ease with which species such as lucidus and hasalis have been 

 able to make use of the nests of recently introduced, nonnatural 

 hosts as Passer domesticus, Fringilla coelebs, Carduelis carduelis, or 

 Turdus merida argues against their having evolved rigid, or even 

 fairly obligatory, host preferences. As may be seen in the following 

 accounts of the several species of glossy cuckoos, there is evidence 

 for some host adaptation, but, with the exception of osculans, the 

 adaptation has not gone very far in a morphological sense. In the 

 relatively "advanced" African species, caprius and klaas, there is 

 strong indication of adaptive egg morphism to several divergent 

 hosts, implying an underlying fixity of host selection, which develop- 

 ment is not to be seen in what is known of the more "primitive" 

 malayanus, lucidus, and basalts groups. 



