LESSON 27.] HAIE. 89 



the Ruminants ; these, however, terminate just prior to the com- 

 mencement of the enlarged portion. This latter at first contains 

 diffused coloring matter (Fig. 148), which soon ceases, and the re- 

 mainder of the hair is transparent. 



457. The quills of the Porcupine (Hystrix cristata) are only 

 modified hairs; all the re- pw 14L pra 



quired tissues being found in 

 these structures, especially in 

 the species quoted. The cu- 

 ticular covering (Fig. 149, a), 

 is seen as a delicate external 

 ring; but by far the most 

 remarkable structure is the 

 cortical substance, which is 



transformed to horn, and Narrow part of the hair, Structure of enlarged por- 



O. paradoxus, tion, O. paradoxus. 



gives amazing strength to the 



quill (b). Press it as hard as you will between the thumb and fin- 

 ger, no impression can be made on it, and to make a thin section it 

 musfc be firstly softened by .p. ug 



boiling. The pigment of the 

 cortical substance is con- 

 tained in a series of well-de- 

 veloped cells (c). The cor- 

 tical layer consists of two 

 structures one (c) made up 

 of cells, possessing pigment ; 

 the other (b) a layer of 

 dense, non-nucleated horn. 



In the centre, and every- 

 where amid the cortical layer, 

 the cells of the medulla (d) 

 are seen. 



458. The quills of the Transverse section Quill of Porcupine. 



English hedgehog (Erinaceous Europeans) exhibit a like structure 

 in a minor degree, but without cuticle. 



Two tissues are there, but the cortical substance descends into 

 the interior of the medullary layer, without reaching the centre 

 (Fig. 150). 



The arrangement of the medullary cells is best seen in a longi- 

 tudinal section (Fig. 151). 



459. Lastly, the American porcupine (Hystrix dorsata) presents 



