28 IMMUNITY IN HEALTH 



However I have not found any clear evidence that 

 definite lymphatic glands — whether interstitial or sub- 

 epithelial — ever occur except in birds and niammals.* 

 Anyhow it is in Ihe internal cleft recesses and the corre- 

 sponding parts of the roof and floor of the embryonic 

 pharynx that the faucial group of lymphoid collections 

 develops, at least in mammals. 



The faucial tonsils usually retain more or less evi- 

 dence of their origin from the second internal cleft 

 recess. Mammalian tonsils t may be roughly divided 

 into two classes : the first, where the principal feature 

 is a protuberant mass of lymphoid tissue partly pro- 

 jecting into the throat ; the second where the principal 

 feature is a blind tube or recess lined by lymphoid 

 tissue and running backwards to open into the throat. 

 (Fig. 6.) But the distinction is one of degree rather 

 than of kind ; for in the projecting tonsils some depres- 

 sion is usually found in the upper part, whilst in the 

 tubular tonsils the lower lip of the orifice is thickened 

 with lymphoid tissue and pouting. Projecting tonsils 

 occur in the following animals : — 



Man (Homo Sapiens), 



Gorilla (Gorilla Savagei), 



Gibbon (Hylohates), 



Hippopotamus (Hippopotamus Aniphibius), 



Dog (Canis Fajniliaris), 



Hairy armadillo (Dasypus Villosus), 



Mouflon (Ovis Miisman). 



Tubular tonsils occur in the following animals : — 

 Grivet Monkey (Cercopitheciis Griseo-viridis), 



* " Specimens of the intestinal canal of both the Skate and the 

 Common Frog have been examined, but did not show any evidences of 

 lymphoid tissue,'' (Berry, 1901.) 



t Mr. Hett found that no tonsil was to be found in a few mam- 

 mals — the Rat, the Beaver, the Porcupine and the Bat, but he showed 

 that the great majority of mammals possessed tonsils. 



