MEMBRANE FORMATION AND CYTOLYSIS 181 
repeatedly, and one hour later placed in hypertonic sea-water 
from which they were transferred to ordinary sea-water after 
thirty to fifty minutes. A number of the eggs which had 
formed membranes developed into larvae. 
These experiments prove that the membrane formation 
induced by soaps can also set up development. This method, 
however, has little to recommend it for practical purposes, 
because the cytolytic effect of the soap is so strong. Eggs 
treated with soap show a much greater tendency to cytolysis 
than those treated with a low fatty acid. 
. Another group of haemolytic agents is formed by fat- 
sotvents, such as benzol, toluol, amylene, chloroform, aldehyde, 
ether, alcohol, ete. It has already been mentioned that when 
benzol, toluol, and amylene are dissolved in sea-water—only 
a trace of them is soluble—they produce a membrane forma- 
tion in eggs, which is followed practically at once by cytolysis. 
Hence the specific fat-solvents are of little use for artificial 
parthenogenesis. The same principle, however, that is found 
in the saponin group also applies here: by working quickly, 
removing the eggs from the benzol or amylene sea-water as soon” 
as membrane formation has taken place, and transferring them 
to ordinary sea-water, it can be demonstrated that a certain 
percentage of eggs form membranes, without undergoing 
cytolysis. These eggs can be caused to develop into larvae 
by treating them subsequently with hypertonic sea-water. If 
they are not treated with hypertonic sea-water, they do begin 
to develop, but they disintegrate before reaching the larval 
stage. : 
Owing to the importance of this subject, we will describe the 
cytolysis of the sea-urchin egg under the influence of a reagent 
belonging to this group. - Figs. 46 to 51 show the behavior of 
the sea-urchin egg in a mixture of 45 ¢.c. of sea-water+5 ¢.c. 
of m/100 salicyl aldehyde. A beautiful membrane formation 
first takes place (Fig. 49); but then cytolysis starts with the 
