708 STRUCTURE OF FEATHERS, HORNS, HOOFS, ETC. 



such as have a downy character, the cellular structure is very dis- 

 tinctly seen in the laminae or ' barbs,' which are sometimes found 

 to be composed of single files of pear-shaped cells, laid end-to- 

 end ; but in larger feathers it is usually necessary to increase the 

 transparency of the barbs, especially when these are thick and but 

 little pervious to light, either by soaking them in Turpentine, 

 mounting them in Canada balsam, or boiling them in a weak solu- 

 tion of Potass. In the feathers which are destined to strike the 

 air with great force in the act of flight, we find the barbs fringed 

 on each side with hair-like filaments or 'pinnae; on one side of 

 each barb these filaments are toothed on one edge, whilst on the 

 other side they are furnished with curved hooks ; and as the two 

 sets of pinna? which spring from two adjacent barbs cross one 

 another at an angle, and each hooked pinna on one locks into the 

 teeth of several of the toothed pinna? arising from the other, the 

 barbs are connected together very firmly by this apparatus of 

 ' hooks and eyes,' which reminds us of that already mentioned as 

 to be observed on the wings of Hymenopterous Insects (§ 528). — 

 Feathers or portions of feathers of Birds distinguished by the 

 splendour of their plumage are very good objects for low magnify- 

 ing powers, when illuminated on an opaque ground ; but care must 

 be taken that the light falls upon them at the angle necessary to 

 produce their most brilliant reflection into the axis of the Micro- 

 scope ; since feathers which exhibit the most splendid metallic 

 lustre to an observer at one point, may seem very dull to the eye 

 of another in a different position. The small feathers of Hum- 

 ming-birds, portions of the feathers of the Peacock, and others of 

 a like kind, are well worthy of examination ; and the scientific 

 Microscopist who is but little attracted by mere gorgeousness, may 

 well apply himself to the discovery of the peculiar structure which 

 imparts to these objects their most remarkable character. 



554. Sections of Horns, Hoofs, Claws, and other like modifi- 

 cations of Epidermic structure, — which may be made by the 

 Section Instrument (§ 137), the substance to be cut having been 

 softened, if necessary, by soaking in warm water, — do not in 

 general afford any very interesting features when viewed in the 

 ordinary mode ; but there are no objects on which Polarized light 

 produces more remarkable effects, or which display a more beau- 

 tiful variety of colours when a plate of Selenite is placed behind 

 them and the Analyzing prism is made to rotate. A curious modi- 

 fication of the ordinary structure of Horn is presented in the 

 appendage borne by the Rhinoceros upon its snout, which in many 

 points resembles a bundle of hairs, its substance being arranged in 

 minute cylinders around a number of separate centres, which have 

 probably been formed by independent papilla? (Fig. 369). When 

 transverse sections of these cylinders are viewed by polarized 

 light, each of them is seen to be marked by a cross, somewhat 

 resembling that of Starch-grains (§ 292 ) ; and the lights and 



