THE VOYAGE OP THE 'CHALLENGER.' 379 



of the dorsal tract ; and this circumstance forms their family character 

 as distinguished from the Longipennes. In the present group the 

 posterior half of the dorsal tract encloses a longitudinal space as far as the 

 caudal pit, dilates a little outwardly on the pelvis, and thus usually becomes 

 united with the very oblique lumbar tracts, and grows rather strong in 

 the simple uropygial band, also covering the base of the oil-gland." 



Nitzsch had no opportunity of examining the pterylosis of Pelecanoides, 

 nor any of the Oceanitidse. His remarks were based on examination of 

 Fulmarus glacialis, Daption capensis, Ossifraga gigantea, Procellaria 

 pdayica, Halobcena ccerulea, Puffinus obscurus, and Diomedea evulans 

 and chlororhyncha. Nitzsch points out certain peculiarities in the latter 

 genus, the most important of these being the division of the dorsal 

 tract into two quite separate parts an anterior stronger part, ending in 

 an interscapular fork, and a posterior, weaker, dilated part. The lumbar 

 tracts he describes as weak and uniserial. I find this division of the 

 dorsal tract to hold good in Diomedea exulans and brachyura, as well as 

 in Thalassiarche culminata, though the break is not very obvious, and 

 chiefly marked by the difference in strength of the feathers. In a 

 nestling of Phcebetria, however, there is no such break apparent ; though 

 the dorsal tract anteriorly is stronger, it passes behind into the posterior 

 part, and the same condition, as is pointed out by Nitzsch, obtains in 

 Ossifraga. The lumbar tracts also can hardly be strictly described as 

 uniserial, as they tend to coalesce, by rows of interposed contour-feathers, 

 with the external borders of the dorsal tract, no very obvious demarcation 

 separating the two. 



Pelecano'ides and the Oceanitidse quite conform to the general type of 

 the group, and indeed the only at all obvious difference in this, beyond 

 those already mentioned, lies in the greater or less amount of the 

 connection between the lumbar and dorsal tracts, this being almost nil 

 in Cymochorea and Procellaria, and considerable in the larger forms, Zo0 ^ Chall. 

 Majaqueus, Puffinus, &c. The knee-gap may become so deep as to pt. xi. p. 16. 

 completely divide the inferior tract into two parts below (e.g. Pelayodroma, 

 Prion, and, according to Nitzsch, Halobcena) *. 



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 

 Diomedeinse it is extremely small, most so in Ditfmedea exulans, where it 



* 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. pi. 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. 



