246 ON THE FORMATION OF 



but chiefly about the head and neck. They are 

 absent from Reptiles, Fishes, and the Molhisca ; but 

 may be observed on many Annulose animals, and 

 even Zoophytes, in which they are subservient to 

 motion. In these inferior classes, however, they 

 appear to be merely filamentous prolongations of 

 the cuticle, and subject to all its changes. This is 

 certainly the case with the hair which is found on 

 many caterpillars, and which separates with the 

 cuticle. But true hair is of a more complicated 

 structure ; each individual hair being provided with 

 a root of a somewhat bulbous form, which is said to 

 take its rise in the cellular web : this, however, is 

 doubtful. Each bulb consists of a vascular and tu- 

 bular portion, and the hair of an external horny 

 covering formed of numerous lateral filaments, and 

 an internal medulla, or vascular pith. The fila- 

 ments of the horny covering are of unequal lengths, 

 those nearest the centre being the longest, so that 

 the hair assumes the figure of an elongated cone, 

 with its base seated in the skin ; this form gives to 

 the hair that peculiar property, on which depends 

 the operation of felting. But there is considerable 

 variation in the form of hairs, in some animals. 

 Thus they are frequently thickest in the middle ; 

 sometimes flat or two-edged, as on the toes of the 

 ornithorhyncus and the common porcupine ; or wa- 

 ved on the margins as in the whiskers of seals. 

 When the hairs are soft and curled they are termed 

 wool ; when straight and stiff, bristles ; and when 

 inflexible spines ; and on the porcupine, quills. 

 Their texture is, moreover, affected by climate and 

 mode of living. Thus in the hog of Siberia and the 

 sheep of Iceland they are long and stiff; in the dog 

 of Malta, and the cat, rabbit, and goat of Angola, 

 fine and silky ; and thin or almost wanting in the 

 dog of Guinea, and sheep of Africa. The colour of 

 hair exhibits very remarkable differences, and na- 

 turalists are at issue as to whether it resides in the 

 fluids of the pith, or in the horny covering. It is, 



