THE TRUE C^OAL APEX, OR THE VERMIFORM APPENDIX. 93 



puitioii, on the other hand, contains a distinct mass of lymphoid 

 tissue in its lateral wall. 



Plate X. 15 illustrates the appearances presented by a longi- 

 tudinal section through the Ciecum of the mouse. The con- 

 striction is well seen, subdividing the cajcum into its basal and 

 apical portions. The mass of lymphoid tissue situated in the 

 lateral wall of the apical portion of the csecum is also a prominent 

 feature of the plate, whilst the basal portion of the ctecum is 

 seen to contain no lymphoid tissue. In the rat the appearances 

 are precisely the same as in the mouse. Plate X. 16 illustrates the 

 appearances presented by a longitudinal section through the 

 caecum of the rat. In this plate the mass of lymphoid tissue 

 situated in the lateral wall of the apical portion is well seen. 



Plate XL 17 illustrates the cffical apex of the European beaver. 

 It contains a large mass of lymphoid tissue situated in the 

 sul)uiucosa, the leucocytes extending inwards towards the lumen 

 of the gut between the Lieberkiihn's follicles. 



Plate XL 18 illustrates the very extraordinary appearances 

 presented by the cffical apex of the Patagonian cavy. The mucosa 

 is transversely striated by a number of ridges, due to the sub- 

 mucosa being heaped up, at regular intervals, into well marked 

 prominences. Each of these contains a large vein, and the 

 muscularis mucosae is well developed. 



In the squirrel, the Egyptian jerboa, and the West Indian 

 agouti, leucocytes are present, but in less quantities than in 

 some of the other rodents. They further show a tendency to 

 be diffused through the mucous coat, and are not specially 

 aggregated together as in the rabbit and the other types 

 examined. 



The rodents examined agree, then, with the results already 

 obtained, in so far that in the mouse, the rat, and the beaver 

 there is lymphoid tissue present in the caecal apex, which is 

 heaped up into prominent masses ; or else the leucocytes are 

 diffused throughout the cteca as in the squirrel, the cavy, and 

 the agouti ; these last leading up to the Patagonian cavy, in 

 which there are no leucocytes. In addition to thus conforming 

 to the previous observations, the Eodentia furnish a new fact, 

 viz., that in the mouse and the rat the lymphoid tissue tends to 

 be specially aggregated together into one part of the caecum 



