346 Stanley and Levns : 



vermiform appendix. We strongly believe that an appendix 

 cannot develop, but that it results as a vestige marking recession 

 from a larger caecum. 



Direct comparison of the rabbit's caecum with man's caecum 

 is impossible, because there is a vast difference between the 

 caecal evolution of man and the caecal evolution of the rabbit. 

 A comparison of the rabbit's caecum with man's caecum is as 

 great an absurdity as a comparison of man's brain with a 

 rabbit's brain. 



Before caecal comparison can be made, a satisfactory basis 

 of comparison must be established. The basis of caecal compari- 

 son must be the relationship in caecal development which the 

 compared anmials bear to their respective natural orders. The 

 rabbit, among the rodents, is distinguished' by enormous caecal 

 development. (Fig- 3.) Man, among the primates, manifests 

 atrophic caecal recession. (Fig. 2.) No primate shows an 

 enormous caecal development at all comparable with the enor- 

 mous caecal development of the rodent rabbit. Among the 

 marsupials we find the koahi (Fig. 19) with enormous caecal de- 

 velopment. Therefore we believe the rabbit and the koala are 

 fit animals for direct comparison. The koala and the rabbit 

 each have the mucous membrane of their caeca raised in ridges 

 for the purpose of absorption ; neither caecum is sacculated by 

 muscle bands. 



The rabbit's caecum and the koala's caecum are both enormous 

 organs, but differ in that the koala's caecum shows no lymphoid 

 gland at the caecal end. Therefore in orderly comparison the 

 rabbit gland turns out to be an arrangement not common, but 

 casual to great caecal development, a glandular arrangement 

 casual to that stage of caecal evolution. 



Although the rabbit's caecum cannot be directly compared 

 with the caecum of a primate, it is possible to institute mediate 

 comparison by' finding a rodent animal in the same stage of 

 caecal evolution as some primate animal. The viscacha and the 

 beaver-rat are sufficiently near the lemur (Fig. 11) to make com- 

 parison between rodents and primates jDossible. Neither the 

 end of the caecum of the viscacha nor the caecal end of the 

 beaver-rat show the lymphoid gland which is obseiwed in the 

 end of the rabbit's caecum. Therefore this lymphoid gland of 



