Jeffries.] 216 [February 7, 



same as in the down-feathers. The ridge of each fold forms the 

 barb, and the sides the barbules and hamuli. In sections the ridge 

 of the fold forms the apex of the triangular section. As in down- 

 feathers the barbules form more rapidly than the barbs. In most 

 cases the barbules are simple rods of elongated cells set end to 

 end. When this is the case they are formed in exactly the same 

 manner as in down-feathers. The barbs also are formed in con- 

 tour feathers in the same way as in down-feathers ; that is, the 

 cells along the ridge of the fold become arranged in a column, 

 and the outer cells of the column become flattened into a coat, 

 while the inner ones retain their original form. The walls of all 

 become converted into horn and the protoplasmic contents finally 

 dry up. 



In the wing feather, as of the common pigeon, where the barb 

 is flattened, the flat portion is formed from the cells in the centre 

 of the fold. The barbules in the wing-feathers are short and 

 arranged nearly at right angles to the barbs. They are formed 

 of transitional cells, which crystalize, to borrow a word from the 

 inorganic world, in the form of the future barbule, with its 

 hamuli. The outer cells become flat and turned into horn and 

 the inner ones into little bladders as in the barbs. A good idea 

 of the change can be formed by examining figs. 13 and 14, in 

 which the shaded portion represents the cut barbs and barbules. 



While the mucous and adjacent cells have been arranging 

 themselves in the form of a rolled up feather, the transitional 

 cells outside have become converted into a sort of connective 

 tissue. This tissue forms a framework which supports the outer 

 parts of the feather, and doubtless represents the various mem- 

 branes described by Cuvier. The pulp within also sends thin 

 laminae in between the barbs. 



Passing now from the shaft and parts of the vane we come to 

 the quill. The formation of this is extremely simple. No folds 

 are formed in the epiderm and as a result the whole remains of 

 one uniform thickness, and is continuous with the shaft and barbs 

 forming the whorl. The mucous and transitional cells of this 

 sheath become converted into threads of horn, while the feather 

 sack and pulp dry up and die. By this means the quill, which 

 is nothing but a tube of horn is formed. The umbilicus is simply 

 the place where the pulp formerly lay. It is commonly stated 



