6 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
After expulsion from the body of the worm the eggs float near the 
surface, where they are immediately fertilized. The eggs are quite 
large ; measurements of the embryos in the 16-cell stage gaye the 
diameter 0.36 mm. The segmentation is total and unequal. Four 
large yolk-laden macromeres are cut off from the four smaller yolkless 
micromeres. These latter then divide repeatedly and overlap the four 
macromeres, and thus the gastula is formed by epibole. Although my 
observations are far too incomplete for anything but general conclusions, 
it appears that the early stages of the segmentation are strikingly 
similar to those of Nereis as described and figured by Wilson (’92). 
Figure 5, Plate 1, represents an embryo in the 16-cell stage, which 
occurs about three hours after extrusion into the water. It will be seen 
that the large macromeres are heavily laden with deutoplasm-spheres, 
while the protoplasm of the micromeres is finely and uniformly vacuo- 
lated, giving the appearance, when seen in sections, of a delicate network. 
The centrosomes are of large size and stain quite deeply in hematoxylin. 
Figure 6 represents the condition of an embryo 94 hours old in which 
the blastopore (4p) is just about to be closed. It will be seen that a 
distinct segmentation cavity (sge) makes its appearance at this stage. 
This cavity may, however, be due to the action of reagents, and may 
not represent the natural condition. Unfortunately, all of my material 
having been killed in Perenyi’s fluid, I am unable to make any state- 
ments concerning this point. It will be noticed that some of the 
micromeres at this stage are beginning to exhibit large intracellular 
vacnoles, This is especially true of those cells about 180° away from 
the blastopore, and also of some in the immediate vicinity of the 
blastopore. In later stages this vacuolization affects all of the cells of 
the embryo, both those of the ectoderm and entoderm, and it is certainly 
true that for the first week of its life the larva owes its increase in size 
almost entirely to the remarkable development of intracellular and 
intercellular vacuoles. In this connection it is interesting to note that 
Davenport (’97) has shown that in the case of tadpoles the early growth 
is almost entirely due to the imbibition of water. Soon after this, when 
the embryo is about 94 hours old the blastopore closes, and the large 
deutoplasm-laden cells are completely enclosed by the micromeres. The 
embryos then become uniformly ciliated and swim about with consider- 
able rapidity. 
Figure 14, Plate 2, represents an embryo 24 hours old. Two eye- 
Spots are now beginning to appear, and between these there is a col- 
lection of greenish-colored cells. These cells stain very deeply in 
