AKT.,19 CONCERNING BIRDS ' TONGUES GARDNER 31 



the genus Passerculus the grooving is very marked so that in some 

 of the species a rolled or tubular tongue is formed (see fig. 137 Pas- 

 serculus rostratus) . 



In conclusion it is obvious that the tongues of birds subserve 

 many different uses, a wide range of function that is paralleled by 

 changes in form, ranging from simple rudimentary nodules of flesh 

 to the highly complex multiple tongues of the flower- frequenting 

 birds. Furthermore, when classified as to adaptations, eight natural 

 groups are formed, to which many of these differing patterns may 

 be assigned. 



The type pattern of tongue is composed of a fleshy basal part 

 which is tipped with a more or less extensive thin horny translucent 

 anterior portion, which has an inherent tendency to curl, bifurcate, 

 and fray laterally. One or all of these tendencies are utilized to 

 produce many adaptive modifications, a fine series of which may be 

 traced through the flower-frequenting birds, where they undergo 

 the greatest development, producing elaborate and complex tubular, 

 brushy, and multiple tongues. 



Fundamentally the tongue is a paired structure arising, as it 

 does, from the second and third visceral arches, and upon this founda- 

 tion must be constructed all the variations seen. Practically, how- 

 ever, in the fully developed organ the alterations have become so 

 great, through fusion of some parts and suppression or exaggeration 

 of others, that it is not possible to select a fundamental pattern from 

 Avhich all others may be derived, but, instead, many of these must be 

 recognized. 



With regard to the taxonomic value of this organ in birds the evi- 

 dence is conflicting. Much of it tends to support the conclusion 

 that it is of little or no value, since, either from similarity of diet 

 or due to convergent evolution, appearances of affinity are formed 

 where no true relationship exists. Furthermore, differences in struc- 

 ture are seen in closely allied birds where presumably the diet is the 

 same. 



On the other hand, in many families, in spite of changes in re- 

 sponse to diet a uniform and characteristic pattern is traceable 

 which gives definite indications of affinity and provides valuable 

 taxonomic features. Among the groups in which this is true are the 

 Ardeidae, Phoenicopteridae, Anatidae, Picidae, Trichoglossidae, 

 Buteonidae, Falconidae, Trochilidae, and possibly the Meliphagidae, 

 Bucconidae, Ramphastidae, Corvidae, and Nectariniidae. To these 

 with more study, others may be added. 



