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animal kingdom, from the lowest protozoa up to the highest 

 vertibrata, man ; and even the extremes meet in some respects, 

 as, for instance, the amseba has its investing membrane, which it 

 tucks in, improvising a stomach when required to absorb its 

 food. Man has also an investing membrane, or skin, and this 

 is directly continuous with the mucous covering on lungs, 

 stomach, and intestines ; it is the external lining pushed in to 

 form the internal, and only changed so far as adaptation to its 

 position requires. 



In the structure of skin, two layers are well marked, viz., the 

 scarf skin, or epidermis, and the true skin, or derma. The epi- 

 dermis is without blood vessels or nerves ; the derma is well 

 supplied with both, hence, the former is a covering of defence 

 to the vascularity and sensitiveness of the latter. The growth of 

 epidermis, and its nourishment, is by inhibition into the nuc- 

 leated cells lying on the papillary eminence of the true skin ; as 

 new ones form, the old cells are pushed to the surface, and are 

 rubbed off as flattened scales. In some animals, as the snake, the 

 entire epidermis is shed at once, and periodically. The physiolo- 

 gical uses of skin in the economy was referred to and explained. 

 The colouring matter of skin lies in the deep cells of epidermis, 

 marking the distinct races of men, as much as the effects of climate. 

 Heat tends to develop an increased growth of pigmentary de- 

 posits. As most living tissues secrete something for the use of the 

 economy in which it is placed, so epidermis has its secretion 

 in the shape of appendages, hairs, horns, hoofs, feathers, scales, 

 nails, and claws. Though so varied, yet all ai*e the same structure, 

 and essentially the same as the membrane that produces them. 



Hairs grow from little pouches in the skin of tucked-in epider- 

 mis; the accumulation of cells push out themselves in the form 

 of a hair. The microscopic appearance of hairs differ in the 

 various animals. The imbrication of the scales are best marked 

 in the bat, approaching in one species to rudimentary feathers, 

 which is remarkable in this flying animal, thus manifesting a 

 continuity of form in these appendages. The medullary part of 

 hairs is well seen in those of the mouse and hare. Such a 

 variety in detail is presented by hairs microscopically, that 

 it is quite possible to determine by it the species of animal from 



