SYSTEMATIC POSITION OF THE PETRELS. 



unusually long, as they conceal all but the terminal sixth of their respective quills. 

 The sixth major covert of the secondary series is slightly shorter than the fifth on 

 the one side and the seventh on the other. 



The sixth covert of the median series is also slightly shorter than the fifth on the 

 one side, and the seventh on the other. The overlap of this series is distal. There 

 are from three to four rows of minor coverts, all having a distal overlap. 



The parapteron and hypopteron in the Procellariidce are moderately well- 

 developed, but the function of closing the gap between the innermost secondaries and 

 the body, during flight, is really performed by the humerals (scapularsj. In the 

 Diomedeidce, however, wherein the humerus is of great length, the parapteron 

 and hypopteron attain their maximum development, and act with, and ancillary to, 

 the humerals (scapulars). 



The oil gland is tufted. The hyporhachis is small. 



The podotheca is covered by irregular hexagonal scutes, except in the case of 

 the two small groups referred to on page xvm, wherein the scutellae are transversely 

 oblique in arrangement. The hallux is vestigial, and is sometimes wanting, as in 

 Pelecanoides. 



The Rhamphotheca is compound, showing a well-defined Laminicorn, Culminicorn, 

 Rhinotheca, and Dertrum. The nasal apertures are paired, and may open on the 

 culmen, as in the Procellariidce, or on either side thereof as in the Diomedeidce. 



The down-feathers in the adult are distributed all over the body : each has a 

 well-developed rhachis and after-shaft. The rami are long, marked by alternate 

 hyaline and pigmented areas, giving a jointed appearance under the microscope. 

 Cilia are rare and minute, visible only under high magnification, and apparently 

 confined to the innermost radii of the proximal rami. These differ markedly from 

 the similar feathers of the Charadriiformes — and therefore from the Laridce, with 

 which, by some authors, the Petrels have been associated. 



Neossoptyles. 



The nestling down of the Tubinares agrees with that of the Sphenisci formes, 

 in that two distinct generations are developed — a protoptyle, and mesoptyle 

 generation — before the appearance of the feathers or Teleoptyles. 



In both Petrels and Penguins the two generations of Neossoptyles follow 

 one another by one continuous process of growth; there is, however, a pause 

 between the two, as indicated by the cessation of rami along the axis common 

 to the two feathers, except in the Albatroses, wherein it is extremely difficult to 

 distinguish the two generations. 



Between the mesoptyle generation and the first teleoptyle generation there 



xvn 



