34 



IMMUNITY IN HEALTH 



caeca of birds (Fig, 7) and m the single caecum of such 

 animals as possess one.* 



Fig. 7. 

 Microscopical section of the small intestine and the two caeca of a 

 pigeon, showing masses of lymphoid tissue in the caeca. The smaller 

 ligure shows the line of section. 

 C.C. Caeca. 

 S.J. Small intestine. 

 L.I. Large intestine. 

 The lymphoid character of the pigeon's caeca is also depicted in 

 plates illustrating Dr. Berry's paper (1901). 



Considering the case of lymphoid tissue in the single 

 csecum one finds, here also, that the different types 

 presented are associated rather with dietetic habits 

 than with phylogenetic position. 



Class A, — The simplest type consists of a mass of 

 lymphoid tissue at the apex of the caecum slightly 



* Berry sectioned the caecal apex in 32 animals and found lymphoid 

 tissue at or near the caecal apex in all warm blooded animals w ith 

 only one or two exceptions. 



