MOULT OF BILL IN THE PUFFIN. 239 
gape, a thick skin, puckered and folded, forms a large rosette of an 
orange-yellow. The appendages of the eyelids consist of a wide, 
thick border of vermilion, and two horny flakes of iron-grey, one 
above triangular, the other beneath elongated (horizontally). 
“Let us now see the aspect presented by the adult Puffin in 
winter, or after the breeding season. 
“The beak is smaller, as if sliced off (¢rongué) in front, and 
especially at the lower mandible, which then forms a broken line 
instead of a regular curve (fig. 2). The two very distinct parts 
which | have pointed out as existing in the adult in spring, may be 
here recognized, the one posterior, strangely modified by the fall of 
the nine horny pieces above-mentioned; the other anterior, which 
has remained unaffected. 
“1. The posterior part has lost somewhat of its thickness and 
consistency ; it is re-covered with a thick skin which presents, on 
the upper mandible (fig. 2), a membranous pleat (a’) and the nasal 
membrane (b’); on the lower mandible, the membranous band (/”) 
and the sheathless chin (9’). 
©, The anterior part has undergone no modification ; it remains 
as it was in the breeding season. 
“The rosette at the gape is reduced to a narrow band of pale 
yellow. The free edge of the eyelid has lost colour, and the horny 
flakes are wanting.” 
Dr. Bureau here furnishes a tableau in which these two con- 
ditions of Fratercula arctica in spring and winter, as well as the 
slight modifications which the plumage undergoes at those seasons, 
are set forth in parallel columns. He then proceeds, under the 
head of “ Transformation du Bec,” to point out the mode in which 
the various pieces of the beak are respectively shed or cast. 
The adult bird, he observes, owes its summer dress to phenomena 
of three kinds—hypertrophy, formation of horn, and coloration ; 
and loses it under the influence of three inverse phenomena, 
namely, atrophy, loss of horny substance, and loss of colour. 
He concludes by showing that analogous phenomena occur in 
the allied species Fratercula glacialis, F. corniculata and Lunda 
cirrata. 
