8 EVENINGS AT THE MICROSCOPE. 



cimens ; they are as transparent and colourless as glass. 

 The imbricated plates project here considerably more than 

 in either of the examples we before examined ; the 

 " teeth," however, form an obtuse angle. 



We shall presently see the importance of this imbri- 

 cate structure ; but we will first look at a few more ex- 

 amples, in which we shall find it still more strongly de- 

 veloped, in conjunction with some other peculiarities. All 

 the hairs that we have looked at are what I have called 

 fibrous in their interior texture, but those of many animals 

 are more distinctly cellular. 



Thus, in these specimens, plucked from the fur of the 

 Cat that lies coiled up on the hearthrug, we see, first, that 

 the imbrications are short, being about equal 

 to the diameter in length, but are very strongly 

 marked ; though, like those of the Sheep's 

 wool, obtuse. Hence the outline is extremely 

 like that of the stem of an old rough palm- 

 tree. There is a distinct bark (cortex), which 

 is thick, and marked with longitudinal lines, 

 which add to the resemblance just alluded to. 

 The interior is clear, marked off at pretty 

 regular intervals by the broad flattened me- 

 dullary cells, in single series, each cell occu- 

 pying, for the most part, the whole breadth 

 of the interior. These cells are transparent, 

 and apparently empty ; but their walls ap- 

 , pear opaque and almost black, an optical 

 illusion, dependent on the absorption of the 

 light by their surfaces at certain angles with 

 the eye of the beholder. The fibrous portion is here 

 almost displaced by the great development of the medul- 

 lary cells. 



In the larger hairs of the Mole, which we will now look 

 at, the bark is very thin ; and though the surface is 

 marked with sinuous lines, these do not project into teeth. 



