438 EDGAR H. NORRIS 



ingrowth of vascular connective tissue) into spheroidal seg- 

 ments, each of which becomes a small sac or follicle whose cavity 

 represents a portion of the originally continuous lumen of the 

 tube. This view has been advocated by W. MuUer (71), Mar- 

 shall ('93 (in chick and frog), Streiff ('97), Prenant ('01), Hert- 

 wig ('10), Prenant, Bouin and Maillard ('11), Broman ('11) and 

 others. Some like Streiff ('97) and Simpson ('12) have de- 

 scribed this branching tubular condition as persisting in part 

 throughout fetal life and even in postnatal life. 



Other investigators, however, have described the lumina of 

 the primary thyroid follicles as appearing directly and ide- 

 pendently, with no preceding tubular stage. The anastomosing 

 soUd cell-cords are usually described as becoixiing varicose, wdth 

 successive enlargements and constrictions, so as to present an 

 irregular beaded chain appearance. Sooner or later each of 

 these spheroidal swollen masses acquires a lumen and becomes 

 separated so as to form an independent follicle. This method 

 of folhcle formation (with no tubular stage) has been described 

 by Tourneux and Verdun ('97), Souhe and Verdun ('97), Gros- 

 ser ('12), Aschoff ('13), Sobotta ('15) and Kingsbury ('15). 



It is impossible to decide from direct observations of sections 

 which of the preceding theories is correct. By reconstruction 

 methods, however, both graphic reconstruction and wax-plate 

 models, evidence has been secured in the present investigation 

 which definitely disproves the tubulai- theory and estabUshes in 

 the human thyroid the independent origin of the lumina of the 

 thyroid follicles. The follicles, however, appear not in epithe- 

 lial 'cords' as described by earlier observers, but in the fenes- 

 trated epithehal plates above mentioned. The view that the 

 thyroid is a modified branching tubular gland (Zielinska, Streiff, 

 Simpson, and others) therefore obtains no support from its 

 morphogenesis, aside from the initial stage of the primitive 

 diverticulum. 



In the glands studied in the present series the fii'st foUicles 

 appear in a fetus of 24 mm. in length (No. 20). This is earher 

 than the time of appearance described by most observers. His 

 ('85), however, described folhcles in a fetus (Zw) whose absolute 



