288 
LILIAN SHELDON. 
Summary of the Results of my Iuvestigatious on the 
Development described in this paper and the 
previous one (4) published in vol. xxviii, part 2, 
of this Journal. 
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 
