CHAPTER III. 



Previous Theories as to the Function of the 

 Tonsils and of the Appendix. 



It is worth while to put aside for a moment the 

 views to be advanced in this book and to consider the 

 previous hypotheses. These hypotheses may be 

 tabulated thus : — 



(1) That the tonsils and appendix are ontogenetic 

 or phylogenetic remnants. Darwin (1874) strongly 

 urged that the vermiform appendix was a vestigial 

 organ, a dangerous and useless relic, which unfortun- 

 ately had not yet been eliminated by the process of 

 natural selection. The idea has always received a 

 large measure of support and demands careful examin- 

 ation. 



A structure is said to be vestigial when it ceases to 

 perform any service useful to the individual. It repre- 

 sents some structure the homologue of which has been 

 of value at some period in ancestral history and which 

 itself may be useful to the individual at some stage 

 of development. Two instances may usefully be given. 

 The actions of the small intrinsic and extrinsic muscles 

 of the pinna of the ear are practically negligible. In 

 some remote progenitor of man they were probably 

 as helpful in picking up and locating noises as they 

 are in the horse to-day. Meckel's diverticulum — of 

 inconstant occurrence in the adult — is another vestige, 

 representing perhaps a primitive intestinal arrange- 



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