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CHAPTER I. 



Introduction. 



After the doctrine of evolution was formulated the 

 values of the various organs in the body were critically 

 examined, and it came to be suggested that structures 

 sometimes persisted in a race of animals long after 

 they had ceased to perform any useful function or 

 indeed any function at all. The question raised is a 

 wide one and has been hotly discussed ; it is usually 

 conceded as a possibility that a structure, especially 

 if it does not become directly injurious, may persist (in 

 a more or less undeveloped form) even when it has 

 ceased to function for generations. Many organs in the 

 body have at one time been claimed to belong to this 

 group of vestigial structures, but with increasing phy- 

 siological knowledge the list steadily shrinks. 



Tonsils, Adenoids, and the Vermiform Appendix are 

 still commonly regarded as useless, even dangerous, 

 relics of a past usefulness (Schafer, 1912). But the 

 investigations recorded in the following pages point in 

 quite another direction, and appear to support the view 

 that these structures (together with the Noduli Lymph- 

 atici Solitaii et Aggregati) should be grouped together 



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