DEVELOPMENT OF HUMAN PHARYNX 331 



first, third and fourth, early becomes ^spread out' or flattened 

 out with but shallow depressions representing it (figures 18-21). 

 This seems clearly to be due to the forward growth and widening 

 of this portion of the pharynx associated with the growth of that 

 portion of the head. It might therefore be possible that the 

 'negative' character of the second pouch is a result of its growth 

 relations; that what became of a pouch or what came out of it 

 was largely a factor of its position; that the determining factors 

 for the 'branchiomeric' organs might be extrinsic rather than 

 intrinsic. My study had not proceeded far before it became 

 evident that, when ultimately interpreted, the entodermic 

 pharynx and its derivatives would have to do considered in 

 conjunction with the growth transformations of the entire 

 region, taking full cognizance of the shiftings due to unequal 

 growth. 



One of the most alluring features of the region is its ancestral 

 character, which is involved in the question of its interpretation 

 and significance. The fact that the mammalian embryo possesses 

 gill clefts, pouches and arches, though never possessing branchial 

 respiration, has been known since the first observations of the 

 mammalian embryo; while the occurrence has been prominently 

 cited as evidence of descent, as one of the most striking illus- 

 trations of the 'Biogenetic law' of Haeckel, of vestigial organs, 

 etc. The present-day attitude, it is true, is inclined to be one 

 of scepticism as to so-called vestigial organs; the recapitulation 

 theory is pronounced a failure in furnishing broad interpreta- 

 tions, while the validity of the 'law' is questioned. 



Sedgwick ('09) in an interesting essay challenges the validity 

 of the 'Recapitulation theory': 



The question at issue is: did the pharyngeal arches and clefts of 

 mammalian embryos ever discharge a branchial function in an adult 

 ancestor of the Mammalia? We cannot therefore without begging 

 the question at issue in the grossest manner apply to them the term 

 'gill-arches' and 'gill-clefts.' That they are homologous with the 

 'gill-arches' and 'gill-clefts' of fishes is true; but there is no evidence 

 to show that they ever discharged a branchial function. The recapit- 

 ulation theory originated as a deduction from the evolution theorj?- 

 and as a deduction it still remains. 



