THE SKIN 



185 



mucus glands, and less uniformly distributed over the sur- 

 face of the body. They are more numerous on the dorsal 

 side of the body and hind legs, and they are especially 

 abundant, and unusually large, in the lateral dermal plicae. 

 According to Junius, they occur on all parts of the skin, 

 although they may be comparatively scarce in certain situa- 

 tions. Like the mucus glands they possess a muscular and 

 a connective tissue coat outside the layer of epithelium. 



M. G M. G 





■^ 



P. G 



Fig. 48. — Section across a dermal plica of Ra7ia esculenta. M. G, mucus 

 glands ; P. G, poison glands ; the granular epithelium has an indefinite 

 outline and shows no cell walls. (After Gaupp.) 



The chief differences in the two types of glands, with the 

 exception of size and the thickness of the tunics, lies in the 

 secreting cells. Engelmann described the epithelium as 

 consisting of cylindrical cells nearly filled with granules. 

 The boundaries of the cells apparently disappear under cer- 

 tain conditions of secretion, the epithelial lining forming a 

 continuous irregular layer of protoplasm (Gaupp). 



The secretion of the poison glands is a whitish fluid with 



