Mr W. Macgillivray oil the Covering of Birds. 261 



miform continuation of the fore part of the tube, which is fring- 

 ed with small barbs ; as in the genus Carbo. In the duck tribe, 

 some species are similar in this respect to the last division, for ex- 

 ample, Anascygnus, leucopsis, albifrons; in others, the accessory 

 plumule begins to exist in a distinct form, but very small, as in 

 Anas tadorna. In the volitant aquatic birdsj as Sula, Larus, 

 Sterna, the plumule becomes distinct, but is still small. In the 

 lobe-footed water birds it also exists in this incipient state, as in 

 Fulica atra, Podiceps cristatus. In the grallatores it attains the 

 length of at least one-third of the feather. It exists in the ge- 

 nus Psittacus, developed in a considerable degree. In the genus 

 Corvus, and the omnivorous birds of Temminck in general, it is 

 commonly about half the length of the feather, but very narrow, 

 and with few barbs. In the genus Turdus, and others allied to it, 

 it is still slender, but nearly two-thirds of the feather in length. 

 In the genus Otis, it is more developed. In the gallinaceous 

 birds it is very remarkable, existing of very considerable size in 

 the genera Phasianus, Gallus, Lophophorus, Polyplectron, Te- 

 trao, Perdix, &c. In these birds it is broad, furnished with 

 numerous tufty barbs, and reaching to about a third of the 

 length of the feather from the tip. In the galhnaceous birds in 

 general, the posterior ventral feathers are downy, and in them 

 the accessory feather is very little shorter or narrower. It is re- 

 markable that the genera Pavo (P. cristatus and P. japonicus), 

 and Crax, have no accessory feathers. This is equally the case 

 with the Columbae. It receives its greatest development in the 

 genera Casuarius and Dromiceius, where it is of equal, or nearly 

 equal, size with the feather itself, and from being downy, has 

 become perfectly similar in structure to it. Whether it exist 

 equally developed in the ostrich I do not know, not having had 

 an opportunity of examining that bird, but it probably does. 

 Yet in the Rhea Americana, a bird closely allied to the emeu, 

 the feathers are all perfectly simple, without even so much as a 

 scale in the place of the accessory feather. I am aware that the 

 double feather has been noticed in the emeu, the cassowary, and 

 the ptarmigans ; but in the other birds which I have mentioned, 

 its existence does not seem to have been known I observe that 

 some writers having seen the double feather in the ptarmigan in 

 winter, have, in a manner that to me seems very strange, taken it 

 for granted that it does not exist in that bird in summer, and 



