THE PHYSIOLOGY OF CELL-DIVISION 705 
fertilized eggs. These abnormalities can in all likelihood be 
largely removed by further experimentation. It is however 
searcely to be expected that any artificial treatment will produce 
such uniform results as natural. fertilization, since the uncon- 
trolled variables are necessarily more numerous in the former 
case. The essential facts are that the after-treatment with hyper- 
tonic sea-water prevents the otherwise resulting cytolysis—an 
effect due probably to a restoration of the normal conditions of 
permeability—and enables the eggs to continue their develop- 
ment to an advanced larval stage. Cyanide has a similar, though 
in my experience less favorable, action. 
Similar exposure to the calcium-containing solutions leaves the 
great majority of eggs essentially unaltered; after remaining 
twenty-four hours in sea-water they appear round and unaltered 
like normal untreated eggs, and on fertilization with spermatozoa 
develop normally. A certain small proportion, however, may 
form membranes under the influence of such solutions; this pro- 
portion is higher with sulphocyanate than with iodide. Thus 
the calcium does not completely suppress though it greatly checks 
the action of the iodide or sulphocyanate. Experiments on the 
permeability-increasing action of these salt solutions confirm 
this conclusion; pigment is slowly liberated in calcium-contain- 
ing iodide and sulphocyanate solutions (more slowly in the former 
than the latter), though the contrast to the rapid action of the 
pure solution is a striking one. Apparently in a small proportion 
of eggs the calcium-containing solutions may ‘effect an increase 
of permeability rapid enough to start development. 
Hence it is usually found that after-treatment with hypertonic 
sea-water produces a small proportion of larvae from such eggs. 
This proportion is of course much smaller than in eggs treated 
previously with the pure solution, but in the case of KCNS may 
be considerable. The majority of eggs, as already stated, remain 
unchanged, and on subsequent sperm-fertilization develop into 
larvee. It should be noted that the above hypertonic sea-water 
acting on normal unfertilized Arbacia eggs for thirty minutes has 
little or no action; a few eggs form membranes and a few un- 
dergo breakdown and an occasional larva may be formed, but the 
