PREVIOUS THEORIES 7 



ment and one which has a direct nutritive function 

 during a part of embryonic life. True vestigial struc- 

 tures are not numerous. An organ of no value becomes 

 a direct encumbrance and will tend to hinder its owner 

 in the struggle to perpetuate its kind. Still the muscles 

 of the auricle and Meckel's diverticulum must be 

 admitted as examples. Is the vermiform appendix 

 such another ? In favour of so regarding it, several 

 observations are made. It varies greatly in size, in 

 position and in the mode of its junction with the 

 caecum. These points however are of little weight : the 

 spleen is more variable in size, all other mesenterial 

 organs vary as much or more in position : whilst in 

 connection with the third point it must be remembered 

 that slight arrests of development are liable to occur 

 even in the most important parts of the body. It is 

 said that the blood supply is poor and hence the 

 occasional gangrene of acute appendicitis. But the 

 intense congestion seen in catarrhal appendicitis com- 

 pletely negatives such a view. In fact the gangrene 

 which may occur is the result of the virulence of the 

 infecting organisms and the absence of collateral cir- 

 culation rather than of the meagreness of blood supply. 

 It is said that retrogression is evidenced by. Its being 

 smaller than other part's of the caecum. Actually, 

 though its lumen is smaller its walls are much thicker 

 and more complex in structure. 



But the two most important witnesses to be interro- 

 gated are Comparative Anatomy and Embryology and 

 their evidence will be taken later (Chapters VIII. and 

 XI.). Suffice it here to say that the tonsil is homologous 

 with a mass of lymphoid tissue in the internal cleft recess 

 of some of the earliest vertebrates, and that the appen- 

 dix is homologous with the lymphoid mass at the apex 

 of the primitive form of caecum, and that in man they 

 show a more highly developed structure than in most 



