442 EDGAR H. NORMS 



the vesicle discharges its contents, collapses and finally re- 

 arranges itself in the form of a number of small acini which 

 repeat the process. 



3. Origin by fusion of follicles. Streiff ('97), v. Ebner ('02), 

 Isenschmid ('10) and others have observed follicles which are 

 apparently formed by the secondary fusion of two or more 

 preexisting follicles. 



4. Origin by division of follicles. Isenschmid ('10) has de- 

 scribed the formation of daughter-folhcles by the growth of an 

 epithelial spur across the lumen of the mother follicle; and 

 Peremeschko ('67) has noted the formation of secondary fol- 

 licles by the constriction of the parent follicle. 



In discussing my observations concerning the formation of 

 secondary follicles in comparison with those of earlier observers, 

 it may be said at the outset that nothing to support either the 

 second or the third methods just outUned has been noted. 

 These, however, have been described chiefly by previous ob- 

 servers upon postnatal material. The other two methods 

 (budding and division of follicles), however, are in general 

 agreement wdth the findings of the present investigation. 



There appear to be three general methods by which secondary 

 follicles arise in the fetal thyroid, the third of which might be 

 regarded as a modification of the second. But each of these 

 types is subject to a mde degree of variation, so that man}- 

 intermediate and modified forms are found. 



1. Solid epithelial buds may develop on the follicle wall (figs. 

 4, 8 and IQd). These may become separated from the parent 

 follicle while in the solid state, or they maj^ develop lumina while 

 connected with the wall of the mother-follicle, and subsequently 

 be constricted off. This method is essentially that advanced by 

 Ribbert ('89), L. R. Miiller ('96), Streiff ('97), and Isenschmid 

 ('10). It is difficult, especially in the earher stages, to distin- 

 guish these solid buds from the 'epithefial tags' representing 

 persistent portions of the original epithelial plates remaining 

 attached to the earher primary follicles. 



2. Hollow buds whose cavities are continuous with that of the 

 mother lumen are alsojound (figs. 4, 9, 10). It might be sug- 



