EXTERNAL PARTS OF BIRDS. —FEATHERS. 
8B 
the casts of the lateral furrows, as well as between each of the minor grooves, and the hollow 
cone would expand into a flat feather-like structure with a median shaft, as a ' vane ' formed 
of ' barbs ' and ' barbules.' In point of fact, in the development of a feather such a cast of the 
dermal papilla is formed, though not in gelatine, but in the horny epidermic layer developed 
upon the mould, and, as this is thrust outward, it opens out in the manner just described. 
After a certain period of growth the papilla of the feather ceases to be grooved, and a continu- 
ous horny cylinder is formed, which constitutes the ' quill.'" (Introd. Classif. Anim., p. 71-) 
Fig. 18. — Symmetrical Figures from Forming Feathers; a, dove; 6, turkey. — " In the summer of 
G9, whilst examining the feather capsule of a nestling dove, the microscopic slide was suddenly covered with a 
ultitude of exquisite forms. . . . The next day my German farmer climbed to the dove's nest and procured a few 
ore pin-feathers. Some of these were cut into fine shreds, rubbed in a drop of water, and placed under the 
icroscope. In a short period the figures of yesterday were again before me. From the cut surfaces of the 
portions of the pin-feathers I had placed under the lens, granules appeared to stream forth like blood, covering 
the microscopic slide in countless numbers. Mingled with these were numerous larger cells of a globular or oval 
form, having a transparent centre. These and the granules gave to the water a slightly glutinous consistency. 
As the fluids on the glass dried, lines at different angles shot across the slide, looking much as though an 
unseen camel's hair pencil had been swiftly drawn in opposite directions, sometimes at right angles, but frequently 
at angles more acute. Probably at the moment of transition from a fluid to a solid condition, the transparent 
nucleated cells assumed the form of a square, a lozenge, a starry hexagon, a cross, or any other beautiful figure 
which could be formed of the parts which suddenly appeared in the spherical cells, these parts seeming at first, in 
some instances at least, to consist of minute triangles. At the same moment the little granules moved to order, 
and there before the astonished gaze were diamonds such as Aladdin might have envied, inform as varied, but far 
more symmetrical, than the frost-work on a window pane of a winter's morning." (Miss Grace Anna Lewis, in 
Am. Nat., V, 1871, p. 675.) 
