956 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 
found that a greater or smaller number of them have formed 
membranes, and have swelled up and cytolyzed. It appears 
to me that this observation can be explained on the assumption 
that the pressure destroys in the egg an emulsion that was 
just near the limits of stability. 
This assumption also explains why occasionally eggs of a 
starfish may develop “spontaneously.” Such eggs probably 
form a fertilization membrane spontaneously. The case is 
similar to the spontaneous segmentation of the sea-urchin egg, 
with this difference, that the sea-urchin egg almost always 
disintegrates after a mere membrane formation, while some of 
the starfish eggs can develop without a second treatment. 
Some authors have stated that ‘‘any stimulus induces the 
egg to develop.” This declaration is of course incorrect for 
the sea-urchin egg, and no authority has stated it for this egg; 
but things of the kind have been credited of the starfish egg. 
The statement is correct within the limits in which it also holds 
for the processes of cytolysis. Cytolysis can be induced by 
very different agencies, including mechanical disruption, cer- 
tain chemicals, heat, and high and low concentrations of the 
solution. The reason for this probably consists in the fact that 
cytolysis consists in the destruction of an emulsion, and that this 
end can be attained by very different methods. — It is, however, 
obviously as untrue to say that ‘any stimulus whatsoever” 
will cause the eggs of the starfish to develop, as it would be to 
assert that every stimulus will cause cytolysis or haemolysis. 
It is needless to say that such an assertion also overlooks the 
role of the second factor in the causation of development. 
The methods of artificial parthenogenesis for the egg of the 
starfish resemble those of the sea-urchin egg very closely. The 
main difference between the two types of eggs exists in regard 
to the necessity of the second factor of fertilization, which does 
not seem to be required in the case of a small percentage of the 
eggs of the starfish. 
