94 THE MICROSCOPE. 



we examine the innermost layer, we mid it soft and 

 granular, consisting of germinal corpuscles in various 

 stages of development into cells, held together by a 

 tenacious semi-fluid substance. This was formerly 

 considered as a distinct tissue, and was supposed to 

 be the peculiar seat of the colour of the skin ; it 

 received the designation of Malpighian layer, or rete 

 mucosum. Passing outwards, we find the cells more 

 completely formed ; at first nearly spherical in shape, 

 but becoming polygonal where they are flattened one 

 against the other. As we proceed further towards the 

 surface, we perceive that the cells are gradually more 

 and more flattened until they become mere horny 

 scales, their cavity being obliterated; their origin is 

 indicated, however, by the nucleus in the centre of 

 each. This change in form is accompanied by a 

 change in the chemical composition of the tissue, 

 which seems to be due to the metamorphosis of the 

 contents of the cells into a horny substance identical 

 with that of which hair, horn, nails, hoofs, &c., are 

 composed."* You will notice, on reference to the 

 figure, that the lower stratum of the epidermis i.e., 

 the Malpighian layer is regularly hollowed out into 

 small depressions, into which the upper surface of the 

 cutis vera rises in the form of little ridges, or papilla, 

 from which nerves and blood-vessels arise. The colour- 

 ing matter contained in the " pigment-cells " is most 

 abundant in the Malpighian layer ; they are generally 

 polygonal in form, and contain a number of extremely 

 minute roundish black granules. I have before me a 

 small portion of the dark-coloured vascular membrane 

 of the eye of a sheep, called the choroid, and see the 

 numerous cells of the layers of pigment very plainly. 

 In dark-coloured races the pigment cells of the skin 



* Carpenter on the Microscope, p. 718. 



