GENERAL ANATOMY. 9! 



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. 256) they became cornified, 

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



S 



It 



I 



FIG. 25B. Many-layered epithe- 

 lium of man. sAt, stratum Mai* 

 pighi ; sc, stratum corneum. 



Flo. 25A. Section through the skin of Petromyzpn Pla- FIG. 26. Single-layered epithe- 

 nerz. ep, the many-layered epithelium of the epidermis, 

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

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

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

 (From Wiedersheim.) 



lium of a snail, c, cuticle ; </,. 

 goblet cells. 



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 



