88 



AXIMAL PHYSIOLOGY. 



[LESSON 27. 



shape of it is very remarkable, and differs from all the other hairs 

 in this respect. The cortical substance is uniformly dark the 



FIG. 143. FIG. 144. FIG. 145. 



Hair of Stag, longitudinal. Hair of Wapeti Deer, longitudinal Hair of Goat, longitudinal. 



result of pigment existing in a diffused condition ; the medullary 

 canal partakes of the same irregularity of form which distin- 

 146. guishes the entire hair, its cells are well shaped, and pig- 

 ment (when not interrupted by air) present. 



454. The hair of the Ruminants (Ox, Sheep, Deer, 

 <&c.) is peculiar ; in them the cuticle cannot be found, be- 

 cause not present ; the cortical substance supplies its place , 

 and the medulla, transformed to large cells, filled only 

 with air, constitutes the bulk of the structure. 



In the Stag (Gervus elephas) the cells of the medulla 

 (Fig. 143) are of great size ; the dark cells are still full 

 of air, which, in small portions, is always intensely black 

 under the microscope ; so too the hair of the Wapeti Deer 

 (Fig. 144) is equally cellular, but of great beauty and 

 smaller size. 



455. In the hair of the Goat the two tissues (Fig. 145) 

 are all that meet our gaze. 



456. The belly of the Duck-billed Platypus (Orni- 

 thorhyncus paradoxus), is covered with hairs of a very 

 curious form (Fig. 146). The bulb, at its extremity, is 

 almost pointed ; the shaft continues its course of nearly 

 equal size for a considerable distance ; at last it becomes 

 attenuated, and gives evidence of terminating (as hairs 

 usually do) in a very fine point. Instead of this, it sud- 

 denly and greatly enlarges, and this continues till it grad- 

 ually diminishes and ends in a fine point. 



At a short distance from the bulb, the narrow portion 

 Hair of is filled with a series of well-formed cells (Fig. 147), like 



O. paradoxus. 



