456 Beebe, Spring Moult of Larus atricilla. [oct k 



or a fresh, perfect teleoptile; never a trace of regeneration of barbs 

 or infusion of new color. 



March 29. — Only three ink-marked feathers are left, the ink 

 being as bright as ever, while in the place of those which have 

 fallen out are the half-grown, slate-colored shafts of the new plum- 

 age. 



. 1 pril 4.— The moult is well toward completion superficially. 

 All the inked feathers have disappeared, and although the new 

 plumage of the dark hood seems dense and full-grown, yet every- 

 where new feathers are sprouting, hundreds showing only as tiny 

 bluish sheaths. The half-grown feathers which are as yet pro- 

 tected by the full-grown ones still show conspicuous white tips, 

 but no trace of this is visible in a casual examination of the un- 

 ruffled surface of the hood; it presents a solid tone of dark slate, 

 except where the few scattered winter feathers still remaining 

 show as flecks of ashy white. 



Examination of the growing feathers under a low power lens, 

 with reference to the white tips, shows that all uniformity in extent 

 is absent, except that the white extends down the vane to an equal 

 distance on each side of the rhachis. In two nearly-grown but 

 unworn feathers, side by side, the white in one is a mere 

 faint distal fringe, while the other is colorless for fully one- 

 third of the vane. In frequent instances a narrow terminal band 

 of normal dark pigment encloses the broader white area, empha- 

 sizing the unstable character of this passing color-phase. 



In scores of feathers, from fully-moulted birds, which I examined 

 under moderately high powers, not one barb showed the slender, 

 transparent, slightly flattened tip which characterizes the abso- 

 lutely unworn barb. So however fresh and perfect the feathers 

 composing the newly acquired hood appear, yet every one has 

 already passed through an important stage of wear. In order 

 to demonstrate fully that the disappearance of the white tips was 

 by wear and not by subsequent infusion of pigment in the growing 

 feather, I inked a number of feathers on the colorless portions and 

 found that the marks invariably disappeared by the time the feather 

 reached maturity. 



During the course of the moult the entire sheath of the mandibles 

 peels off; in one case a large piece coming off at once, showing the 

 fresh horn beneath bright carmine in color. 



