PLATE 3 



EXPLANATION OF FIGURES 



25 to 35 Cross sections, 6m thick, of a 7 mm. embryo. Note the medium of at- 

 tachment of duct and ectoderm and its obvious origin from the former. In figure 

 30 the cytoplasm of the cell is a thick layer, attached to the ectoderm at only two 

 points. This and figure 31 show the irregular form of the growing tip, which be- 

 comes more regular as it frees itself from the ectoderm. Figures 33 to 35 show 

 mitotic figures in the ectoderm, those in figures 33 and 34 being in metaphase with 

 the axis of the cell corresponding with that of the ectoderm ; that in figure 35 being 

 at right angles to the same axis. The anlage of the duct is attached to the ecto- 

 derm by clear cytoplasm, which, in figure 35, seems to have contracted and pulled 

 the ectoderm out of line. 



36 to 39 Consecutive cross sections of a 10 mm. cmbi'yo, presenting much the 

 same features as the last series, except that the duct is larger and the connection 

 between it and the ectoderm is not so close and it becomes free more abruptly. 



368 



