58 



X. Observations on the Structure of Bats' Hair. By John Quekett, 

 Secretary to the Microscopical Society. 



Read October 20, 1841. 



Of the endless variety of beautiful objects disclosed to us by means 

 of the microscope, the hairs of different animals are not amongst 

 the least interesting, and of these none excel in beauty of structure 

 those of the bat tribe. It is to some peculiarities observable in the 

 structure of the hair of these curious animals that I would direct 

 the attention of the Society for a short time this evening. In order 

 to make the subject more intelligible to those who may not be familiar 

 with the formation and growth of hair, these few explanatory remarks 

 may not perhaps be out of place. " Hair," says Mr. Hunter, " is of 

 two kinds respecting its growth. One is that w r hich grows continually, 

 or has the power of growing continually if not allowed to grow to its 

 whole extent, or when allowed to grow to its full extent, although it 

 then becomes stationary, yet is capable of growing when cut. The 

 second kind grows until it arrives at its full extent, and then cut or 

 not cut it must be shed, and, like feathers, must be replaced by ano- 

 ther growth. Most animals have both sorts, but man I believe has 

 only the first. The tail and mane of the horse are of the first kind, 

 whilst the hair which covers the body is of the second."* 



It is to hair of the second class that my observations will be prin- 

 cipally directed. According to physiologists hair is developed in 

 highly vascular sacs or follicles, situated in the cutis or true skin, and 

 each hair commences at the bottom of the follicle by a swelling, 

 termed the root or bulb : this is softer than the rest of the hair, and 

 is hollow, and contains within it the pulp of the hair, which is pro- 

 bably a vascular prolongation of the bottom of the follicle ; and each 

 hair is formed by the successive aggregation of cytoblasts or new 

 cells, and is gradually protruded from the follicle, both by the growth 

 and elongation of its constituent cytoblasts and by the addition of 

 new layers of these to its base, the apex and shaft of the hair being 

 formed before the bulb, just as the crown of a tooth is before its fang. 



The cytoblasts are round and loose at the base of the hair, but are 

 more compressed and elongated in the shaft ; and by this rectilinear 

 arrangement the hair assumes a fibrous character. 



* Huntcrian Manuscript Catalogue. 



