268 LILIAN SHELDON. 



Summary of the Eesults of my Investigations on the 

 Development described in this paper and the 

 previous one (3) 



1. The ovum is heavily charged with food-yolk; the seg- 

 mentation is on the centrolecithal type; the protoplasm is 

 mainly at one pole of the egg, and in this protoplasm nuclei 

 arise, probably by the division of the segmentation nucleus. 

 The protoplasm forms a loose reticulum containing nuclei on 

 the surface of the egg, which first extends over only a small 

 area, but later spreads over the surface until, in the latest 

 stage which I have, it covers about half the periphery of 

 the egg. 



2. In the latest segmenting ova there are small masses of 

 protoplasm in the centre of the egg, which masses sometimes 

 contain nuclei. 



3. Shortly after the segmentation begins the yolk becomes 

 divided up into a number of rounded segments, which, however, 

 bear no relation to the true segmentation. 



4. The central nuclei of those lying just beneath the peri- 

 phery multiply mnch more rapidly than those over the rest of 

 the ovum, thus coming to form a special area, which finally 

 extends along about the middle third of the ovum, and consists 

 of a loosely-reticulate mass of protoplasm containing a large 

 number of nuclei, and having in transverse section an irregular 

 triangular shape. Nuclei are present through the rest of the 

 ovum, being more numerous near the periphery than the 

 centre. 



5. The triangular-shaped protoplasmic area becomes more 

 compact and flattens itself out, forming a plate-like mass of 

 protoplasm densely packed with nuclei on the surface of the 

 middle third of the ovum. This plate is the blastoderm. The 

 nuclei over the rest of the egg have undergone no change. 



6. The blastoderm grows round the ovum till it covers about 



