426 EDGAR H. NORRIS 



long axes, in their final position, are at right angles to their origi- 

 nal position in the plate. As a result of this shifting process, little 

 circlets (really spheres) of nuclei are formed in the plate. 



This shifting of nuclei is but the visible expression of the 

 changed position of the cell. For while it is impossible to ob- 

 serve the cell boundaries in most cases, it is hardly probable 

 that the nuclei shift their axes independent of the cytoplasm; 

 moreover, the few faint cell-boundaries which may be made out 

 show the same changes in position as do the nuclei. Further, it 

 is usually found that at the point from which a nucleus has 

 shifted toward the center of the plate a slight depression appears 

 on the surface of the plate, indicating that the cytoplasm has 

 shared equally with the nucleus in the movement. From these 

 three facts it may be concluded that the first process manifested in 

 foUicle formation is the shifting of the axes of certain cells of the 

 epithelial plate through an arc of 90 degrees. There is no evidence 

 that the depressions on the surface of the epitheUal plate are due 

 to invasions or activity of the adjacent mesenchyme (fig. 3). 



This process results in the transformation of the smooth sur- 

 faces of the bands (fenestrated plates) into surfaces which are 

 somewhat roughened. The irregularities are apparently not, at 

 first, due to swellings on the plates, but rather to the slight in- 

 dentations produced by the shifting of certain cells toward the 

 center of the plate as above described. When studied in cross 

 sections (fig. 2) such a plate appears as a sort of beaded chain, 

 with alternate swellings and constrictions. But, as noted 

 above, the initial swellings due to this process are only apparent 

 and are actually not greater in thickness than is the plate in 

 other parts of its extent where indentations have not yet 

 occurred. 



The extraordinary cellular activity of the epithehum at this 

 stage is clearly manifested by the large number of mitotic figures 

 to be seen. There is no section of the gland in the 24 mm. 

 fetus (No. 20) which does not present several cells in process of 

 mitosis. But the localization of these mitoses is even more sig- 

 nificant than is their number. It will be noticed that the 

 nuclear figures are usually found only in those places in the 



