MEMBRANE FORMATION AND CYTOLYSIS 183 
outflow of a clear substance from the cytoplasm (Fig. 50), 
and soon after the egg is changed to a shadow (Fig. 51). 
In this case also the process of cytolysis is divided into two 
stages, at first, a membrane formation, and soon after a complete 
clarification of the interior and the formation of large clear 
drops (Fig. 51). 
If the eggs are placed in a mixture of 10 c.c. of sea-water-+ 
10 c.c. 24 m propylalcohol, the formation of a fertilization mem- 
brane is the first thing that takes place. If the eggs are removed 
Fig. 52 Fig. 53 
Fries. 52 and 53.—Membrane formation and cytolysis in two different eggs 
of a sea-urchin under the influence of propylalcohol. In Fig. 52 cytolysis starts 
with the outflow of many small droplets; in Fig. 53 with the outflow of only one 
large drop from the cytoplasm. 
from the solution at this stage, and washed with sea-water, a 
few are able to develop after a subsequent exposure to hyper- 
tonic sea-water. 
But if the eggs are left in the solution of alcohol, cytolysis 
quickly ensues. Figs. 52 and 53 show the start of this cytolysis 
which in the one case consists in the outflow of many clear drops 
from the egg, and in the other of one large drop. At bottom, 
it only depends upon two modifications of the same process. 
It may be mentioned that the result of the experiment remains 
the same if 1 ¢.c. of 24 m NaCl is added to each 4 ¢.c. of propyl- 
alcohol. 
5. We come now to a discussion of the cytolytic action of 
distilled water. This type of cytolysis is of great importance 
