LESSON 28.] EPITHELIUM. 93 



465. A form of hair, from the larva of an insect (Dermestes lar- 

 darius) very common in larders in this country, is so curious in form, 

 that it were unpardonable to omit it ; moreover, it tends to show the 

 great display of Almighty wisdom, even in the construction of a 

 hair ! Two figures of this hair are given, as seen by different mag- 

 nifying power, and in different conditions ; the first (Fig. 160) is per- 

 fectly spear-shaped, the imbrications being most distinct : this is mag- 

 nified 300 diameters. In the second figure (161) the head of the 

 spear is opened like an umbrella, a state in which these hairs are fre- 

 quently found ; it is now magnified 500 diameters. 



466. The larva (upon whose body these hairs are alone found) 

 does not exceed three-eighths of an inch in length, and appears to be 

 a very quiet, passive animal. Whatever use it makes of these most 

 remarkable hairs remains unknown, no one has even hazarded a con- 

 jecture in relation to them, notwithstanding there can be no reason- 

 able doubt that they are defensive, as those of Aphrodita are offen- 

 sive. Let the reader only imagine what the effect would be on 

 another animal, advancing to molest the larva of Dermestes, and 

 have all these hairs suddenly porrected (stretched forth), and the 

 umbrella-like processes suddenly opened in its face ! 



The foregoing demonstrations have distinctly proved firstly, the 

 general character of imbrications as common to a majority of hairs ; 

 secondly, the important fact that hair, in man and most of the higher 

 animals, consists of three distinct tissues ; and, thirdly, that where a 

 tissue is lost (cuticular layer), it designates, most usually, the smooth 

 (non-imbricated) hairs. 



LESSON XXVIII. 



EPITHELIUM. 



467. On the external surface of the body we found the skin pro- 

 tected by a layer of flattened horny scales, called Epidermis ; this 

 layer is continued over the outer surface of the lips, lining the whole 

 interior of the mouth, covering the surface of the tongue, descending 

 into and lining the (Esophagus, Stomach, and Bowels, but, in conse- 

 quence of its altered form, under the new name of Epithelium. 



468. This peculiar tissue is also found covering all other Mucous, 

 Serous and Synovial membranes ; it lines the heart, blood-vessels and 



