50 = ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 
When in the spring of 1887 my brother and I performed experi- 
ments upon the fertilization of sea-urchin eggs, we had before us the 
question as to what influence the concentration of sperm exerted upon 
the polyspermous fertilization of injured eggs, and especially those 
whose life functions had been interfered with through treatment with 
reagents. Thus eggs were treated for thirty minutes with a 1 per cent 
solution of strychnin and then mixed with sperm of the same species 
at various dilutions. In one case the sperm was so much diluted with 
sea-water that on the evidence both of observation in the living con- 
dition and of a very thorough examination of preserved material more 
than 90 per cent remained unfertilized owing to the addition of insufti- 
cient sperm. Fifty minutes after fertilization the control material 
was preserved. As before, 89 per cent of them were unfertilized. In 
these I found the beginning of an interesting change, which I will 
here describe: 
Briefly, this alteration consisted in the fact that the nucleus 
showed changes similar to those occurring after fertilization. 
The division processes started in the nucleus, but, “in the 
majority of cases a nuclear or cell division did not take place. 
In exceptional cases a single division of the egg into two cells 
occurred, and each of these was provided with a nucleus. These 
cases which approach nearest to a normal division process are 
rare, and they also differ from the normal” (p. 44). Later 
Hertwig convinced himself that the longer sea-urchin eggs had 
Jain in sea-water without the addition of sperm, the more of 
such divisions incidentally occurred. We shall later return to 
this phenomenon. 
In 1892 the writer! found that if the freshly fertilized eggs 
of a sea-urchin (Arbacia) are brought into hypertonic sea-water 
(about 100 c.c. of sea-water-+2 g. NaCl) the eggs do not divide 
in such a solution; but if they are returned to normal sea-water 
after two, three, or four hours, in quite a short time, after twenty 
or even ten minutes, the egg breaks up into several cells at 
once; and indeed the longer the eggs remain in the hyper- 
tonic solution, the greater the number of the cells into which 
' Loeb, ‘‘ Experiments on Cleavage,’’ Jour. Morphol., MIT, 253 18g2. 
