16 THE VOYAGE OF H.M.S. CHALLENGER. 
Majaqueus, Puffinus, &e. The knee-gap may become so deep as to completely divide 
the inferior tract into two parts below (e.g., Pelagodroma, Prion, and, according to 
Nitzsch, Halobena).} 
The hypopterum is usually well-developed, with long feathers, and the humeral tracts 
are very strong and broad. 
The contour-feathers always have an after-shaft, though in the Diomedeinze it is 
extremely small, most so in Diomedea exulans where it is reduced to a short tuft, about 
half an inch long, of five or six nearly simple, straight plumes. In the smaller Albatrosses 
it is larger, and in the rest of the group, including Pelecanoides, it is of good size. 
All the forms have their spaces as well as tracts covered by down-feathers, which 
may become very long and close-set, especially in Pagodroma. 
The oil-gland is always large, globular, with its surface covered above at the base— 
which is also partly covered by the termination of the uropygial band of the dorsal tract— 
by scattered semi-plumes, and with a tubular mamilla, provided with a good tuft of 
down-feathers. The tuft and gland are never absent. In the Oceanitidee and smaller forms 
(Cymochorea, &c.) the tuft of feathers simply encircles the apex of the gland, but in the 
larger ones it sends a median prolongation across it as well, so as to divide the surface 
of the mamilla into two lateral parts, separated from each other by the median row of 
feathers, and each with its opening or openings. The number of these varies in the 
different forms of the group, as already indicated by Nitzsch (loc. cit., p. 144). Diomedea 
exulans has about half a dozen small ones in each half, arranged in a crescent. Diomedea 
brachyura and Thalassiarche have numerous small apertures opening into a single large 
circular common opening. The Fulmars, except Aezpetes, have several apertures in each 
half, as have Daption and Pagodroma, Ossifraga having as many as five. Majaqueus 
has four; Zstrelata three. Aeipetes, Pelecanoides, Bulweria, and the smaller Procellariide, 
as well as the Oceanitidee, have apparently only two pores, one in each half of the gland. 
The very young birds, I may remark, are, in all the species I have seen, covered with 
a thick coating of fluffy grey down, which is pushed off as usual at the ends of the 
contour-feathers when the latter appear. There are apparently no intermediate changes 
of plumage, the first plumage of the young bird being similar to that of the adult,’ a 
condition of things very unlike that in the Gulls (Laridze) with which the Tubinares have 
so often been associated. Besides the long down on the tracts corresponding to the 
future tracts of contour-feathers, the young birds have a shorter downy covering 
distributed pretty uniformly, as in the adults, over the intervening spaces, and between 
the feathers of the tracts. 
1 Nitzsch lays some stress on the angle, whether acute or obtuse, made by the lumbar tracts at their junction with 
the dorsal ; but the difference in the direction of the two parts is not, as seen in entire birds, so obvious as would be 
judged from Nitzsch’s figures (loc. cit., pl. x. figs. 2, 3), which were probably made up from the examination of skins 
only. The lumbar tracts, where the connecting rows of feathers are best developed, seem always to run outwards and 
backwards from the dorsal tracts, as shown in his figure of Puffinus obscurus. 
2 Diomedea exulans may be an exception. 
