CHAPTER XI 



Life History of the Subepithelial Lymphatic 

 Glands. 



The records of comparative anatomy show that the 

 subepithelial lymphatic glands occur almost if not quite 

 exclusively in the two highest classes of animals — birds 

 and mammals. It is in accordance with this fact that 

 we find these structures appearing late in human em- 

 bryological history. Follicles of lymphoid tissue do not 

 appear in the tonsil till the last month of foetal life, 

 though the epithelial crypts are represented as early as 

 the fourth month (Keith, 1913). Berry, ir. 1901, stated 

 that the lymphoid tissue in the ca^cal region of mam- 

 mals was almost entirely a post-jiatal development and 

 that it attained its maximum growth at the end of the 

 first week. 



To confirm this observation I examined the appen- 

 dices of three young rabbits similar in size and appear- 

 ance, and from the same litter. One was killed within 

 an hour or two of birth, the second on the fourteenth, 

 and the third on the twenty-eighth day after birth. 

 Sections of the three appendices were taken and stained 

 in precisely the same way and were drawn with the 

 same camera lucida, eye-piece and objective, and are 

 represented in Fig. 25. It will be seen that the 

 lymphoid tissue can hardly be discerned in the newly- 

 born rabbit, but that its development is very rapid in 

 the first few weeks after birth. When we remember 



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