MATURATION OF THE EGG 247 
such as an acid must be formed before the one or more enzymes 
necessary for development can be activated, we can under- 
stand that the absence of this substance must lead to a pause in 
the life-cycle of the organism. The introduction of this sub- 
stance from without, or the initiation of its production within, 
the cell will then effect development. 
It may be well to remember also in this connection that 
the unfertilized eggs of purpuratus can be induced by a hy- 
pertonic solution to segment into two or four cells, without 
developing further. They go into a resting stage again, from 
which they can be aroused by causing artificial membrane 
formation. It would be very important to know why these 
eggs did not go on developing after they had started to 
segment under the influence of the treatment with a hyper- 
tonic solution. 
3. It appears to be very generally the case that maturation 
can be induced by treating eggs in the oocyte stage with sodium 
hydrate; for I have obtained results similar to those recorded 
for Polynoe, with the eggs of Nereis, and also of Sipunculus. 
Unripe eggs which refused to mature in sea-water did mature 
when exposed for a few hours to hyperalkaline sea-water at 15°C. 
With regard to the maturation of the eggs of Nereis at Pacific 
Grove, I made an observation that may perhaps be important 
from the point of view of the mechanism of maturation and 
membrane formation. In the immature egg of Nereis there 
is a greenish-blue pigment distributed evenly over the entire 
surface. This pigment layer contains many small, highly re- 
fracting droplets which may be fat particles. On treating 
the eggs with hyperaikaline sea-water, so that they mature, 
the following changes are observed: first, a membrane is lifted 
up, comparable to the fertilization membrane of the sea-urchin 
egg; second—but long after membrane formation—the numer- 
ous droplets (fat?) flow together into a few large drops; third, 
the greenish mass, which had previously formed an even layer 
