I.] 



SEGMENTATION. 

 FIG. 7. 



21 



SURFACE VIEW OF THE GERMINAL Disc OF A HEN'S EGG 



DURING THE LATER STAGES OF SEGMENTATION. 



(Chromic Acid Preparation.) 



At c in the centre of the disc the segmentation masses are 

 very small and numerous. At b, nearer the edge, they are 

 larger and fewer ; while those at the extreme margin a are largest 

 and fewest of all. It will be noticed that the radiating furrows 

 marking off the segments a do not reach to the extreme margin 

 e of the disc. 



The drawing is completed in one quadrant only ; it will of 

 course be understood that the whole circle ought to be filled up 

 in a precisely similar manner. 



In this way, by repeated division or segmentation, 

 the original germinal disc is cut up into a large number 

 of small rounded masses of protoplasm, which are small- 

 est in the centre, and increase in size towards the peri- 

 phery. The segments lying uppermost are moreover 

 smaller than those beneath, and thus the establishment 

 of the two layers of the blastoderm is foreshadowed. 



