22 The Bird 
The first intimation of the appearance of a feather, or 
of down, is shown by a thickened group, or pimple, of 
cells in this under layer of skin, which grows and presses 
upward toward the outer layer—the epidermis. This is 
exactly the way in which the scales of fishes and reptiles 
begin to form; and if, at this stage, the tiny projection 
should flatten out, the shining scale of a carp, the armor 
Fic. 11.—Sprouting feathers of a 12-day embryo chick. Magnified 25 diameters. 
of an alligator, or the cobble-scale of an iguana lizard 
might result. Indeed, in the feathers of a penguin we 
find transition stages of flat, almost unsplit feather- 
scales; while on the legs and feet of birds are reptile-like 
scales. 
The evolution of scales, hair, and feathers is a most 
interesting problem, most of the details of which are 
beyond the scope of this work. Suffice it to say that 
