1920.] Study of Nestling Birds. 857 



and are afterwards replaced !)}■, plumules. These are found 

 ill tlie young of many, though not ail, tlie species that 

 possess plumules in adult life, [n structure pre-peniise and 

 pre-pluinula3 are often indistinguishable. 



Tcleoptiles. — Acomprehensive term for all contour-feathers. 

 Newton (Dictionary of Birds, p. 243) includes adult down or 

 plumules in his definition of this term, but its application 

 is iiere restricted to contour-feathers. 



Mesoptiles. — Semi-plumous feathers, forming an inter- 

 mediary [)lumage or second generation of feathers. These 

 are found in adolescent individuals of a few species (Barn- 

 Owl, etc.) and are acquired between the first generation 

 of nestling down (neossoptiles) and the adult plumage of 

 contour-feathers (teleoptiles), and the term is here used 

 in tliis restricted sense. Pycraft does not thus confine its 

 application, but uses the word for all the forms of nestling- 

 down immediately preceding teleoptiles. His assumption 

 seems to be that all nestling birds originally developed two 

 distinct generations of pre-pennse down and that in the 

 majority of species the first generation (which he calls 

 " proto[)tiles^^) has now been suppressed"^. 



Neossoptiles or NestUng-doivn are comprehensive terms 

 used in this paper to denote the existing first generation of 

 down-feathers, and is applied to these whether succeeded by 

 mesoptiles or directly followed by teleoptiles, or whether 

 pre-penna3 or pre-pluinulse. 



Fig. I, showing the pteryla3 of the neossoptiles in 

 a nestling Pied Wagtail {Motacilln lugubris), gives the 

 nomenclature I intend to adopt for the diftei-ent down tracts 

 mentioned in this paper. It will be noticed that this nomen- 

 clature differs only slightly from that used by Ticehurst 

 (Brit. Bds. Mag, vol. ii.), and later by Witherby in his 

 ' Practical Handbook of British Birds.' For reasons already 

 explained (Brit. Bds. Mag. vol. xiii. p. 78), 1 have sub- 

 stituted "capital tract" for their "-inner supraoi'bital tract," 



* A study uf the nestling pluui;i>^e of some of the llajjtores suooests 

 tluit, in some cases at any rate, it is the second and not the first oenera- 

 tion of nestling-down that has been suppressed {cf. fig. 17, p. 875). 



