THE MICROSCOPE IN ANIMAL HISTOLOGY. 219 



deeper part of the nasal cavity, we find nucleated cylin- 

 drical cells taking the place of ordinary ciliated epithe- 

 lium, and sending processes downward, which communi- 

 cate with each other, forming a delicate network (Plate 

 XXI V, Fig. 175). Between these cells we find the olfac- 

 tory cells, spindle-shaped nucleated bodies, extending up- 

 ward into a fine rod and downward into a varicose fila- 

 ment. In birds and amphibia these rods are terminated 

 by delicate hairs, some of which have ciliary motion. 

 Beneath these structures are peculiar glands, consisting 

 of pigmeuted gland-cells. They are called Bowman's 

 glands. The branches of the olfactory nerve proceed be- 

 tween these glands and branch out into fine varicose fila- 

 ments, which are supposed to communicate with the 

 olfactory cells. Hardening in chromic acid, or Muller's 

 fluid, or a concentrated solution of oxalic acid, or one- 

 half to one per cent, solution of sulphuric acid, is neces- 

 sary for the preservation of these delicate structures. 



d. Organs of Sight. As in the sense of touch certain 

 tactile papillae detect deviations from the general surface ; 

 and in that of taste special rod-like end organs and their 

 covering bulbs distinguish the solutions of different sapid 

 substances ; and as in smelling, not the whole organ but 

 olfactory regions, with peculiar cells and nervous rods, 

 discriminate mechanical or chemical odors, so in vision a 

 special apparatus is provided to perceive the wonderful 

 variety of colors and forms. The minute structure of 

 organs becomes more complex in proportion as they serve 

 the higher functions of mind. 



The various tunics and accessory structures of the eye 

 are described in most text-books ; we here limit ourselves 

 to a brief reference to those refracting and receptive struc- 

 tures w^hose office it is to translate the phenomena of light 

 into those of nervous conduction. 



Externally, we have in front of the eye the transparent 

 cornea. This is made of connective tissue with cells, bun- 



