T72 STUDIES IN GENERAL PHYSIOLOGY 
the unfertilized eggs of sea-urchins. It would be of interest 
to determine whether such an ion when it is found also brings 
about an agglutination of the sea-urchin eggs. 
In other forms, Nereis, Podarke, and Phascolosoma, the 
experiments have been carried far enough so that we can say 
that artificial parthenogenesis (swimming larve) is possible in 
these. The experiments, however, have not yet been worked 
out sufficiently in order to allow them to be published. 
We can say with certainty of the methods given here that 
they lead to successful results in the American forms on the 
Atlantic ocean. In the attempt to discover new methods it 
may perhaps be well to keep the following (theoretical) con- 
siderations in view, which I have discussed in greater detail 
in various earlier papers. The artificial methods for obtain- 
ing parthenogenesis must be able, first of all, to favor the 
liquefaction or other destruction of the nuclear membrane. 
Secondly, they must also alter in a definite way the physical 
properties of the protoplasm (viscosity, etc.). It seems that 
in the eggs in which artificial parthenogenesis has succeeded 
thus far (and possibly in many, if not all, other eggs) chemical 
changes take place under natural circumstances in the unfer- 
tilized egg, which endeavor to alter the egg in the two direc- 
tions mentioned above; that these, however, under ordinary 
conditions occur so slowly that the egg dies before it under- 
goes actual cell-division. Those circumstances which are 
able to accelerate these natural processes will also bring about 
the development of the unfertilized egg. 
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