ARTIFICIAL PARTHENOGENESIS IN ANNELIDS 675 
into sea-water whose osmotic pressure has been raised by the 
addition of KCl (e. g., 88 c.c. sea-water + 12 cc. 24n KCI), 
and if after two hours they are put back into normal sea- 
water, they will develop into swimming larvae. In this case, 
as a rule, only one embryo develops from an egg, and dwarf 
larvee are an exception. If, however, instead of KCl the 
corresponding quantity of NaCl or MgCl, is added to the 
sea-water, as a rule more than one embryo originates from 
one egg, and larve of normal size are rare. I have not 
made many experiments with CaCl,, but it seems to act 
more like KCl than like NaCl. In the experiments in which 
the osmotic pressure of the sea-water was raised by cane- 
sugar, dwarf blastule were also observed. 
I have already mentioned in an earlier paper that the 
lack of a membrane favors the origin of more than one 
embryo from the unfertilized egg. The fertilized egg has a 
membrane which keeps the cleavage cells together. But if 
the membrane be destroyed, the egg may give rise to more 
than one embryo. In a small number of unfertilized eggs 
the treatment with KCl gives rise to a very thin film, which 
may act as a membrane and prevent the cleavage cells from 
becoming separated. But such a fine film is lacking in the 
majority of eggs treated with KCl (or CaCl,) in the right 
proportions to produce parthenogenesis. And yet we do not 
notice the falling apart of cleavage cells which in the case of 
the NaCl eggs or MgCl, eggs leads to the formation of more 
than one embryo from an unfertilized sea-urchin’s eggs. 
The observation of the process of cleavage shows that the 
treatment of the eggs with KCl increases their power of 
adhesion. The various cleavage cells of a K egg stick to- 
gether, while after a treatment with NaCl the cleavage cells 
adhere much less to one another and fall apart. The same 
tendency is produced by the addition of MgCl, to sea-water. 
It is quite possible that the relative amount of the various 
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