DEVELOPMENT OF HUMAN PHARYNX 381 



Through a succession of functions whose bearer remains one and the 

 same organ, is accomphshed the Transformation of Organs. Each 

 function is a resultant of several components of which one constitutes 

 the chief or primary function while the others represent accessory 

 or secondary functions. The subsidence of the chief function and the 

 rise of an accessory function alters the total function. The total function 

 becomes a different one and a result of the transformation is the Trans- 

 formation of the Organ (p. 60). 



Dohrn at this time did not apply his principle to the pharyn- 

 geal derivatives. He subsequently, however, in his ' 'Studies 

 of the development of the lower vertebrates," stated his conclu- 

 sions (a) that the thyreoid represents a pair of branchial pockets 

 located between the first and second in the present series (Studies 

 VII, VIII) ; (b) that the hypophysis is developed from a preoral 

 pair of branchial clefts (Study II); and (c) that the thymus 

 (in sharks) is developed out of dorsal portions of the gill pouches 

 which form gill lamellae, but, being overlaid by dorsal branchial 

 musculature, become cut off and grow to form the thymus (Study 

 IV) . The first two interpretations are, I think of purely historical 

 interest at the present day. 



Willey in his interesting book on "Amphioxus and the ances- 

 try of the vertebrates" clearly faces the question of the inter- 

 pretation of the glands, which his central theme brings in for 

 comparison, namely, the thyreoid (p. 169), the thymus (p. 29) 

 and the hypophysis (p. 283) ; and as clearly recognized the prin- 

 ciple of the "change of function." In the case of the thyreoid, 

 the regressive element is recognized in that the ''ductless gland" 

 (the thyreoid) is a "vestige of the very actively functional 

 endostyle or hypobranchial groove of the Ascidians, Amphioxus 

 and Ammocoetes." He does not propound any 'principle,' 

 however, nor does he discuss the matter in detail or more broadly. 



Wiedersheim ('03), on the other hand, in a paper on "The 

 aging of organs in the race history of man and its influence in 

 disease processes," clearly recognizes a genetic principle involved 

 and its broad significance for pathology. The endocrine organs 

 are considered, but only as having their place in a larger concep- 

 tion. I desire to translate two passages: 



