72 Bulletin Wisconsin Natural History Society. [Vol. 10, Nos. 1 & 2. 
added, and allowed to remain for about twenty-five minutes, nearly 
all of them, when transferred to normal sea water, underwent 
development. Some progressed as far as the blastula stage, while 
others developed to the gastrula phase, and a few developed into 
plutei. 
The membrane was also called forth when sea urchins eggs 
were placed into sea water that was saturated with a hydrocarbon, 
such as chloroform, benzol, toluol, and the like. Unless the eggs 
are very shortly removed to a hypertonic medium of sea water, 
cytolysis sets in. If this is done, and the eggs, after being acted 
upon by the concentrated solution for about twenty-five minutes, 
are again transferred to normal sea water, many of them will 
develop into plutei. 
The eggs of starfish, worms, and mollusks, when subjected to 
the same treatment, were also found to undergo partial develop¬ 
ment. The fertilization membrane was evoked in each case. 
From these experiments it seems that either one of the fol¬ 
lowing two conditions are necessary for bringing about the arti¬ 
ficial parthenogenesis of eggs: 
1. The cytolysis of the cortical layer of the egg, by means 
of which a protein membrane, which, in all probability is lipoidal 
in nature, is formed, and, 
2. The action of various hypertonic salt solutions. 
Loeb, in the starfish, showed that the formation of the yolk 
membrane, alone, was sufficient to cause the egg to develop a 
normal larva. He therefore regards the membrane formation as 
the essential thing in fertilization. Uoeb, Edler, Mathews and 
others have shown that the yolk membrane in echinoderm eggs 
may be produced through irritation, as when Ast'erias eggs are 
touched or dropped into sea water, or through the blood of Chce - 
topterus or Sipunculus, or through normal salts, or as has been 
recently shown by many investigators, through crosses between 
two different species of lower organisms. These last named 
crosses are commonly designated as “heterogeneous crosses.” 
