428 EDGAR H, NORRIS 



at the periphery of the circle and form a dark band, which 

 surrounds an expansive, clear, central cytoplasmic portion. 

 The magnitude of this cytoplasmic area and the sharp contrast 

 between the two portions (in the stained preparations) are 

 usually striking features (fig. 3). It is in the center of this cyto- 

 plasmic area that the lumen makes its appearance as a tiny 

 spherical space outlined by a definite and regular margin. It is 

 as though the cells had but drawn a little apart, so that their 

 central ends, instead of remaining in contact one with another, 

 might be separated by an interval. The relation of the early 

 lumina to one another is well shown in figure 6, which is a 

 graphic reconstruction of a plate. It is important to note that 

 no tubular stage is found in the process of lumen formation. 

 The lumina appear as absolutely independent spaces. 



As the lumina first appear they apparently have no content; 

 but undoubtedly they contain some substance which is not 

 stained with the ordinary methods, and which increases in 

 amount with the size of the follicular cavity. Certain of the 

 larger lumina (not all of them), which are perhaps older, are 

 found to contain a hazy, granular substance. Typical colloid 

 does not appear until later, in the 60 mm. stage (No. 40). 



The various possibilities as to methods by which the follicular 

 lumen may arise will be considered later in the discussion. 



Fig. 6 A graphic reconstruction (surface view) of parts of two fenestrated 

 epithelial plates from the thyroid gland of a human fetus 30 mm. long (No. 30) 

 to show the relative position of the lumina {Fol.L.) as they appear in the plate. 

 Lumina indicated by stippled areas. Note that in all cases these early lumina 

 are quite distinct and never connected with one another. Per/., perforation. 

 X 267. 



Fig. 7 A graphic reconstruction of a number of epithelial masses from the 

 thyroid gland of a human fetus 60 mm. long (No. 40). Note the various degrees 

 in the breaking up of the plates and the relative positions of the lumina. a-b 

 indicates level of section in figure 5. X 267. 



Fig. 8 A graphic reconstruction of a follicular complex shown in the lower 

 part of figure 17. Lumina indicated by stippled areas. Note the solid buds. 

 X 267. 



Fig. 9 Model (reconstructed by Born's wax-plate method) of a large follicle 

 from the peripheral part of the lateral lobe of the thyroid gland in a human 

 fetus 60 mm. long (No. 40). The three buds shown have lumina communicat- 

 ing with the lumen of the main follicle. X 267. 



