CHAPTER VIII. 



Comparative Anatomy of the Subepithelial 

 Lymphatic Glands. 



It is not easy to obtain accurate data on this branch 

 of the subject. Sohtary and aggregated lymphatic 

 nodules vary much in size and visibility according to 

 their activity and the age of the individual. It is 

 often impossible to distinguish human Peyer's patches 

 with the unaided eye. . Microscopical assistance is 

 necessary : yet very little histological investigation has 

 been imdertaken. 



The following imperfect account of the comparative 

 anatomy of these glands has been drawn largely from 

 the facts recorded by Berry (1895 and 1901), Hunting- 

 ton (1903), Stapley (1911) and Seccombe Hett and 

 Butterfield (1910 and 1913), which have in some in- 

 stances been confirmed by the present author. 



The three main groups — namely the iaucial, the ileal 

 and the csecal — are represented in most if not all the 

 higher animals. Each group must be considered in 

 turn. 



The Faucial Group is arranged round the fore part 

 of what represents the primitive pharynx. In the walls 

 of the fish's pharynx, which is highly developed sub- 

 serving gill respiration, wandering amcebocytes can be 

 seen, and " thymus glands " have been described in 

 the dorsal diverticula of all the gill slits. 



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