GENERAL ANATOMY. gi 



here to replace an equal quantity of worn-out cells (Fig. 

 25A). 



In the course of this change of position, the proto- 

 plasmic bodies may undergo an alteration ; in the reptiles, 

 birds, and mammals (Fig. 2515) they became cornified, 

 i.e., first the borders, then the inner part of the cell, 



2? 



-So 



Co 



FIG. 258. Many-layered epithe- 

 lium of man. sM, stratum Mal- 

 pighi ; sc, stratum corneum. 



Flo. 2SA. Section through the skin of Pttromyzpn Pla- FIG. 26. Single-layered epithe- 



neri. ep, the many-layered epithelium of the epidermis, Hum of a snail. <:, cuticle ; d^ 



including B, goblet cells ; Ko, granular cells ; Ko. Co, goblet cells, 

 dermis (with blood-vessels G), consisting of bundles of 

 fibrils running horizontally (W) and vertically (5.) 

 (From Wiedersheim.) 



change into horn. Of the living cell there remains for 

 some time still the nucleus, until at length this vanishes, 

 and then the cell becomes completely changed into a dead, 

 horny scale. In the skin of the higher vertebrates the 

 zones of the living protoplasmic, and the cornified cells 

 no longer capable of life, are sharply marked off from one 



