INTRODUCTION. IX 



general results are more or less of little value, but the consideration of them 

 taken as a whole is of great value when the superficial characters are well 

 understood. 



Pterylosis is not well known at present, so that definite conclusions 

 cannot be recorded, the only point to emphasise being the continual examina- 

 tion of specimens and that criticism of results will later follow. All we now 

 know is that variation is seen when not anticipated and consequently 

 commonly misunderstood, and the present facts are not of great significance 

 through ignorance of basic data. It is a subject that will repay continued 

 study, but not occasional excursions. 



Another item continually quoted is the presence or absence of the oil 

 gland, and whether it be nude, tufted or feathered. The absurdity of the 

 usage of such a character should be obvious. However, it has been seriously 

 put forward as of value, but its true insignificance is now generally accepted. 

 The presence or absence of the aftershaft and its size are also mentioned, but, 

 of course, that character has also been minimised through better material 

 and more study, as species which have been commonly cited as showing no 

 aftershaft prove to possess one. 



A peculiar feature of the wing feathering was noted, and immediately 

 investigated as of import, but here again its absolute value cannot yet be 

 appreciated. We refer to the loss of the fifth secondary, though its covert 

 is present. This state of the wing has two alternative terms, quincubital 

 or eutaxic and aquincubital or diastataxic. The comparative value of this 

 state is well seen among the Swifts, where both forms occur. More valuable 

 as an absolute character is the coloration of the nestling from the egg onward. 

 The state of the nestling when it emerged from the egg was once utilised, 

 but this seems of less value than the coloration of the first feathering. That 

 this is extremely important is at once seen by study of downy nestlings of 

 the Scolopacine group. It is always necessary to remember that secondary- 

 results are apt to obscure hasty examination in connection with many of the 

 above features, but the only conclusion possible from an unprejudiced viewpoint 

 is that there are no internal features of outstanding importance, the exceptions 

 being so numerous, and the main items so imperfectly investigated ; while 

 external characters show less variation and are better known and their develop- 

 ment can be more perfectly studied through the much greater mass of material 

 available. Consequently throughout this work we have given full details 

 of the external features, and also added the internal items as commonly 

 given in text books for the benefit of workers the former all being drawn 

 up from actual specimens, and therefore accurate ; the latter compiled from 

 various authoritative sources, and only in few instances, as yet, verified by 

 ourselves. 



Before we leave this subject we may enter an apology as to the genus 

 splitting complained of in connection with our work. We have given a 

 description of the generic characters observed, and have endorsed these with 

 a beautiful painting of the character noted. When we have studied all the 



