EXTERNAL PARTS OF BIRDS. — FEATHERS. 



83 



uiulerlying dermal layer of iuteguinent. This central mass is the pulp which is to nourish the 

 rapidly growing feather ; it becomes a soft spongy network and furnishes the blood supply, but 

 is not otherwise transformed into the substance of the feather. For the latter is entirely epi- 

 dermal, being built up from the cells of that portion of the Malpighian stratum which covers 

 the central pulp. This portion subdivides into three layers. The outermost layer sprouts out 

 of the skin in the form of a horny cylindric sheath, and is the well-known object we call a 

 " pin-feather." The thick intermediate layer m,akes most of the feather itself, set free when 



Fio. 18. —Symmetrical Figfures from Forming Feathers; a, dove; 6, turkey. — "In the summer of 

 18G9, wliilst examining the feather capsule of a nestling dove, the microscopic slide was suddenly covered witli a multi- 

 tude of exquisite forms. . . . The next day my German farmer cUmbed to the dove's nest ainl procured a few more pin- 

 feathers. Some of these were cut into fine shred-s, rubbed in a drop of water, and placed under the microscope. In a 

 short period the figures of yesterday were again before me. From tlie cut surfaces of the portions of tlie pin-feathers I 

 had placed under tlie lens, granules appeared to stream forth like blood, covering the microscopic slide in countless num- 

 bers. 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 ditferent angles 

 shot across tlie slide, lookmg much as though an unseen camel's hair pencil had been swiftly drawn in opposite directions, 

 sometimes at riglit 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 wliich suddenly appeared in the spherical cells, these parts seem- 

 ing at flrst, in some instances at least, to consist of minute triangles. At tlie same moment the little granules moved to 

 order, and tliere before the astonished gaze were diamonds such as Aladdin might have envied, in form as varied, but far 

 more symmetrical, than the frost-work on a window pane of a winter's morning." (Grace Anna Lewis, Am. Nat., v, 1871, 

 p. 675.) 



