392 THE FUR SKALS OF THE PRIBILOF ISLANDS. 



fornica. The body is densely covered with down, that of the head and neck being 

 blackish, but profusely spotted with white. The white down is less fluffy and is gener- 

 ally longer than the dark, esiiecially on the neck, where it is yellowish. When the 

 young murre emerges from the egg, much of this down is still in the sheaths and all is 

 damp and wiry. As the bird dries, this becomes separated and fluffy, but with the 

 long white and yellowish downs this drying is slower than in the other. Thus until 

 separated each tuft of down appears as a single part and may sometimes be seen as 

 shown in fig. 9, PI. XLI, where a tuft is held in the center by the persistent remains of 

 the sheath. In fig. 10 will be seen one of the tufts sheathless but not separated, and the 

 tip, really composed of many, appearing as a single piece. The black down soon 

 becomes dry and fluffy, but the longer white tufts remain as an apparent single growth 

 for sometime except on the throat and face, where it is soon separated by the move- 

 ments of the young bird in rubbing its throat and neck on the rocks. Though to the 

 eye these long, yellowish, pointed downs appear as single, under the microspope they 

 are found to consist of six or more, as shown in fig. 11, where a tuft is beginning to 

 separate. As the new plumage appears it is seen that these bunches of down are 

 attached to the tips of the growing nestling feather, but the constant rubbing of the 

 youngster against the rocks and its parent causes the greater number of these downy 

 parts as they grow out to break off', so that when the bird is three or four weeks old 

 but few remain, and these mostly on the back of the neck. These, however, do not 

 appear as tufts but as filaments, each attached to the tip of a ramus of the new grow- 

 ing feather, as shown in figs. 16 and 17. At the point of apparent juncture there can 

 be seen a slight swelling (a, fig. 14), which is greatly enlarged (a, fig. 18). Instead of 

 the downy tufts separating, they are often held together around their bases by a some- 

 what persistent part of the sheath through which the down grew, or by a gluing 

 together (figs. 12 and 13). In such cases friction soon removes all at once from the 

 tip of the growing feather. Therefore it will be seen that the tuft of down has no true 

 rachis of its own, only the temporary one of the sheath. And the i)arts into which 

 the tuft can be divided are only elongations of the rami of the first true plumage 

 feather, as shown in fig. 14. The bunch or swelling is formed, I believe, in this way. 

 The down grows to its full length before the young murre is hatched. Then the longi- 

 tudinal growth ceases, but cell making continues and causes the part at or near the 

 surface of the skin, being soft, to swell. Then after a few days the new feather begins 

 to appear, slowly at first but steadily, until the downy stage is all pushed out and its 

 place occuj)ied by the entirely different first-plumage feather.' Sometimes several of 

 these downy tips will remain attached to the tips of their respective rami, the whole 

 being held together at the swellings by a sticking or joining (fig. 15). Usually the 

 downy tip breaks off' below the swelling, but often above, so that it ends some of the 

 rami of the new feather, but occasionally the break occurs in the center of the swell- 

 ing (fig. 18). The same process obtains in the case of the underbody feathers but 

 varied somewhat in the belly feathers. Here the joined bases of the downy tufts 

 appear double, as shown in fig. 19. These are numerous and somewhat persistent 

 until separated by the movements of the bird, plus the growth of the new feather. 

 But these downs are not readily broken off, so that they persist attached as filaments 

 to their respective rami much longer than those on the back, except the ones on the 

 back of the neck, which are the last to be lost. It is curious that these last persist in 



' The swelling is found in many birds which I hope to illustrate later. 



