Coloration of the Mouths and Eggs of Birds. 

 Text-figure 6. 



293 



Transitional nestling tongues. A and 0, of Prima mgstacea, B, of 

 Cisticola cinerascens, illustrating the evolution of tlie three-spot and 

 the twin-spot tongues from, prohably, a generally dusky tongue. 

 The figures should be studied in oonjunction with Mr. Collingwood 

 Ingram's (' Ibis,' Oct. 1907, p. 575). The continued presence of 

 scattered black-pigment cells, even on the cleared portion of the 

 tongue, is interesting, as is their linear arrangement in the Prinia. 



Another interesting point, previously overlooked, is Mr. 

 Bates* observation to the effect that Cisticola erythrops, even 

 when adult, never loses the twin spots. Both observations 

 have a possible bearing on the question, Are the spots a 

 nestling adaptation? and the first may be used as an argu- 

 ment in favour of that view, seeing that some (but not all) 

 of the mouths concerned turn black again when the nestling 

 stage is over. 



EXPLANATION OF PLATE VII. 



Fig. 1. Amhlyospiza albifrons, vaoviilx oi n&&t\mg. 



Fig. 2. Coliuspasser ardens, mouth of nestling. Fig. 3. Mouth of 



adult. 

 Figs. 4 and 4 a. Lagonosticta rhodopareia, nestlings. Fig. 4 i, mouth 



of adult. Fig. 5, mouth of young. 

 Fig. 6. Cisticola natalensis, mouth of fledged nestling ; 6 a, of younger 



nestling ; 6 b, tongue only of intermediate stage (for adult 



see fig. 12). 

 Fig. 7. Estrilda astrild, head of nestling. 



