VERTEBRATED ANIMALS. 267 



menopterous Insects are locked together ( 638). Feathers or portions 

 of feathers of Birds distinguished by the splendor of their plumage are 

 very good objects for low magnifying 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 Microscope; 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 Humming-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 theseVbjects their most remark- 

 able character. 



664. Sections of horns, hoofs, daws, and other like modifications of 

 Epidermic structure, which can be easily made by the Microtome 

 ( 184), 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 FIG. 454. 



a more beautiful variety of colors 

 when a plate of Selenite is placed be- 

 hind 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 resem- 

 bles a bundle of hairs, its substante 

 being arranged in minute cylinders 

 around a number of separate centres, 

 which have probably been formed 

 by independent papillae (Fig. 454). 

 When transverse sections of these 

 cylinders are viewed by polarized 



light, each of them is Seen to be Transverse section of Horn of Rhinoceros, 



marked by a cross, somewhat resem- viewed b y Polarized Light, 

 bling that of Starch-grains; and the 



light and shadow of this cross are replaced by contrasted colors when the 

 Selenite plate is interposed. The substance commonly but erroneously 

 termed whalebone, which is formed from the surface of the membrane 

 that lines the mouth of the Whale, and has no relation to its true bony 

 skeleton, is almost identical in structure with Ehinoceros horn, and is 

 similarly affected by polarized light. The central portion of each of its 

 component threads, like the medullary substance of Hairs, contains cells 

 that have been so little altered as to be easily recognized; and the outer 

 or cortical portion also may be shown to have a like structure, by macer- 

 ating it in a solution of potass, and then in water. Sections of any of 

 the Horny tissues are best mounted in Canada balsam. 



665. Blood. Carrying our Microscopic survey, now, to the elemen- 

 tary parts of which those softer tissues are made up, that are subservient 

 to the active life of the body rather than to its merely-mechanical re- 

 quirements, we shall in the first place notice the isolated floating cells 

 contained in the Blood, which are known as Blood-corpuscles. These 



