Coloration of the Mouths and Eggs of Birds. 277 



in the direction of Motacilla ? Again, in depending for 

 distinctiveness on the contrast to a dark background of its 

 two bright rows o£ palatal papillae, the mouth of Macronyx 

 croceus (figs. 19, 20) resembles to that extent the mouth 

 of the Bearded Tit (the actual appearance must be very 

 different owing to its lacking the latter's black patch); 

 yet the two birds are not related. The mouth of Cisticola 

 cinerascens (fig. 10) also much more resembles that of Prinia 

 mystacea (fig. 8) thaa it is like that of its own congener, 

 C. natalensis (figs. 6, 12), the result of a quite different 

 ground-colour. There is a strong likeness between the 

 mouth-coloration of Pycnonotus layardi (figs. 15, 38), 

 Hyphantornis jamesoni (figs. 13, 18), and a Chrysococcyx 

 (fig. 14), parasitic on the latter, yet no affinity is present. 

 The three Bulbuls already mentioned have a bright or deep 

 flesh-red mouth, yet another, Phylhstrophus flavigula, has 

 an orange mouth, and yet another, Andropadus latirostris, 

 has it yellow. 



Meaning of the distinctive coloration of nestlings' movths. — 

 The only explanation attempted up to the present, so far as 

 I am aware, has been that of directive markings, on the 

 analogy of the explanation given for certain markings in 

 flowers. Mr. D. Seth-Smith, at the B. O. C. meeting at 

 which I first stated my results, mentioned the semi- 

 luminous, bead-like blue warts which are present on the 

 sides of the base of the mandibles in the nestlings of certain 

 species of birds, such as the Gouldian Grassfinch (Poephila 

 mirabilis) and the Parrot-Finches (Erythrura). He remarked 

 that these appeared to be necessary in order to indicate to 

 the parent-birds where to place the food. When feeding, 

 the parent stood in the entrance-hole of the nest, excluding 

 almost all light, and in this position the nestlings were 

 nearly invisible; but when their mouths were opened these 

 could be easily located by the presence of the blue beads, 

 which were placed, as it were, at each corner of a square. 



It seems to me exceedingly probable that the function of 

 the blue beads in these and other species is directive, and 

 that usefulness for directive purposes may, at any rate, have 



