VII 



EPITHELIUM 



109 



FIG. 28. Columnar epithelial cells 

 from the Frog's intestine. 

 (X 500.) 



m. droplet of mucus exuding 

 from cell : nu. nucleus. 



of the intestine into the smallest possible particles, it 

 will be found that the process has detached numerous, 

 minute, conical bodies, about 

 polygonal in transverse sec- 

 tion, and having one end flat 

 and the other more pointed 

 (Fig. 28). These bodies are 

 called epithelial cells : in the 

 natural position they lie closely 

 cemented to one another, like 

 the blocks of a wood-pavemept, 

 their flattened ends facing the 

 cavity of the intestine, while 

 their narrower ends abut against the connective-tissue 

 layer (p. 70). Thus the epithelial cells together form an 

 epithelium or epithelial layer of the mucous membrane 

 directly bounding the cavity of the enteric canal. 



Each cell consists of protoplasm and contains a 

 rounded, granular nucleus (nu), which is made very 

 conspicuous by staining, and in which are 

 one or more small bodies or nucleoli. Cer- 

 tain of these cells have a space towards 

 their free ends containing slime or mucus, 

 and thus have the form of little cups or 

 goblets : they are known as goblet-cells 

 (see right hand cell in Fig. 28). 



Ciliated Epithelium. By the same 

 method the mucous membrane of the 

 mouth is also seen to be lined by an 

 epithelium, but the cells comprising it 

 (Fig. 29) are broader in proportion to their 

 length, and' each is produced on its free surface into a 

 number of delicate, transparent threads of protoplasm 

 called cilia, which in the living condition are in constant 

 movement, lashing backwards and forwards like minute 



FIG. 20. Ciliated 

 epithelial cells 

 from the mu- 

 cous membrane 

 of the frog's 

 mouth, (x 500.) 



(From Parker's 

 Biology, after 

 Howes.) 



