THE TRUE C^CAL APEX, OR THE VKRMIFORM APPENDIX. 87 



That this iucrease in the aiuouiit of the lymphoid tissue is 

 not present in other parts of the alimentary canal is well shown 

 in PI. VII. 4 from an adult cat, and also in PI. IX. 9, which repre- 

 sents a transverse section through a small intestine of a kitten, 

 and which section was specially prepared as a check observation 

 on the development of the lymphoid tissue in the csecal apex of 

 the kitten. As check observations, numerous sections were cut 

 through the small and large intestine of both cat and kitten, 

 but nowhere was there this same accumulation of lymphoid 

 tissue found as in the csecum. Further, in all cases the sudden- 

 ness with which the lymphoid tissue ceases at the junction of 

 ciBcum with large intestine constitutes a very marked feature 

 of tlie various specimens examined from both cats and kittens. 



An examination of the microscopic structure and develop- 

 mental history of the csecum of the cat confirm, then, in every 

 detail, the results obtained from the rabbit. In both the cat 

 and the rabbit there is a most marked accumulation of lym- 

 phoid tissue at the true ciecal apex, an accumulation which 

 reaches its maximum growth within one v,^eek after birth. 



AvES, — Golutnba livia, the Pigeon. 



In the pigeon there are two short cteca, which open into the 

 general intestinal canal at the junction of small and large gut. 

 Figure 2 illustrates diagrammatically these short caeca, and also 

 shows the sites of the various sections to be immediately 

 described. PI. IX. 10 shows a low-power view of the microscopic 

 appearances presented by a longitudinal section through the 

 intestinal canal, and one of the two short c^eca of the pigeon. 

 It will be seen that the walls of the Ccecum are merely masses 

 of lymphoid tissue collected into germ centres, whilst the 

 general intestinal canal contains but little lymphoid tissue. The 

 contrast between the relative amounts of lymphoid tissue con- 

 tained in the caecum as opposed to that of the intestine is as 

 striking a feature here as in the two previous types examined 

 — the rabbit and the cat. 



An examination of the two short cieca of the pigeon confirms 

 the general results already arrived at in the rabbit. It further- 

 more especially proves that in the pigeon the whole of the csecal 



