76 



GENERAL PRINCIPLES OF ZOOLOGY. 



the nucleus remains for some time, 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 another. In cross-section they are 

 readily distinguished as the stratum corneum (sc) and the stratum 



2? J3 



J} 



riS' 



Fio 27 — stritilied epithe- 

 lium of man sV stratum 

 Malpighi, 6c, stratum 'cor- 

 neum. 



Fig. 26.— Section through the skin of Petrominon 

 planeri. Ep, the many-layered epithelium of the 

 epidermis, including B, goblet cells ; Kn, granu- 

 lar cells; Jvo, (V), dermis (with blood-vessels 

 G), consisting of bundles of fibrils running hori- 

 zontally ( FD and vertically (S). (From Wiedcrs- 

 helm.) 



Fiu 2b — Sill gU-la-i ered 

 epithelium of a snail. c. 

 cuticle ; rf, goblet cells. 



Malpighi (sM) of the skin (fig. 27). In the many-layered epithelia 

 the cuticle has lost its importance, and it is cither an inconspicu- 

 ous boundary line or is entirely absent. 



Glandular Epithelium.— Glandular epithelium is distinguished 

 physiologically from ordinary pavement epithelium by the fact 

 that it also produces secretions or excretions; anatomic:il]y it is 

 recognizable by the presence of ' gland cells," cells which carry on 

 tlie secretion and, to a greater or less extent, reveal their character 

 by their structure. Ciharactcristic glandular cells are, for example, 



