440 EDGAR H. NORRIS 



surrounded by epithelial cells. But in no case in the present 

 observations was 'colloid' found within the very early follicles; 

 although the accumulation of some other (precolloidal?) secre- 

 tory product between the angles of the cells, might result in 

 lumen formation. The fact is that the smaller lumina, which 

 are probably the most recent in formation, have been univer- 

 sally found to be devoid of any demonstrable content, and that 

 some of the larger and supposedly older lumina do contain a 

 stainable substance. As to the nature of the precolloidal sub- 

 stance or substances, nothing definite is known. 



One might suggest (as thought by His?) that the lumen could 

 be formed by a degeneration or hquefaction of the central ends 

 of the cells which later form its outhne. In this case it would 

 be expected that the early follicles would present a lumen out- 

 lined by an irregular or ragged margin. Without exception, 

 however, the lumina of the early follicles are clearly outlined 

 and marked off by a very sharp margin. 



Having studied the way in which the follicle forms within the 

 plate, it is of further interest to determine the method by which 

 the follicle frees itself from the plate and comes to take up an 

 isolated existence. Earlier observers, in describing the forma- 

 tion of follicles from anastomosing rods or tubes, have laid em- 

 phasis upon the activity of the adjacent mesenchymal tissue as 

 the factor operating in the separation of the follicles. In the 

 present study no definite morphological evidence appears in 

 favor of this view. For as shown in figure 3 there is no special 

 differentiation of the mesenchyme or increased vascularity in 

 the regions in which follicles are being separated off from the 

 plate. The evidence seems rather to indicate that the follicles 

 themselves are the active agents in their separation. Thus as 

 certain of the cells leave their original positions to assume a 

 position more nearly in the center of the plate, the indentations 

 previously described appear on the plate. These may be con- 

 sidered as weak points. And as the cells increase in number 

 between these indentations it is not difficult to see how the in- 

 creased pressure due to the increased mass might force certain 

 follicles out from the row in which thev formed and thus iso- 



