432 MANIPULATION. 



Hairs. — These are very readily obtained from all the higher 

 animals, their presence may even be detected in the whale 

 tribe when young. The smaller kind of hairs may be mounted 

 either dry or in fluid, when of a dark colour, Canada balsam 

 is to be preferred ; to obtain a satisfactory view of the struc- 

 tiure of large hairs and spines, horizontal and vertical sections 

 should be made by the machine described at page 336. Pre- 

 vious to being mounted, the hairs should be perfectly cleaned, 

 as more or less greasy matter is always present about them ; 

 ether should be employed as the cleansing fluid, the hairs 

 being made dry by pressing them between folds of blotting- 

 paper. Care should be taken to select both the hair and the 

 wool from each animal, as they difier materially in their 

 structure, the finer kind, or what is known as wool, being 

 endued with the property ienaeA felting , which property varies 

 in different species of animals, that of the beaver and nutria 

 possessing it in the highest degree. AU hairs are composed 

 of an aggregation of epithelium cells, and the colour depends 

 upon the quantity of pigment deposited in or about each cell; 

 on this account, some of the most delicate have been used as 

 test objects, specimens of which are figured in plate 6, and a 

 description of each given in the chapter devoted to that 

 subject. Hair is employed in most cases as a protective 

 coating, in others as an organ of touch, whilst in a still fewer 

 number, when occurring in the shape of spines, it serves the 

 purpose of a weapon of defence ; of this latter, the horn of the 

 rhinoceros, the quills of the porcupine, the spines of the 

 Diodons, are famihar examples, they, like scales and feathers, 

 being modifications of the dermal skeleton. The minute 

 structure of the hairs of different species of the same genus 

 or family is so constant, that a practised eye can readily 

 discriminate between them ; several valuable papers on this 

 subject have been pubHshed by Mr. Busk, in vols. i. and ii. 

 of The Microscopic Journal. A list of many remarkable hairs 

 of insects and Crustacea has already been given at page 418. 

 The following animals wiQ exhibit the most characteristic 

 specimens that can be obtained from the vertebrate classes : — 



