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LOEB. [Vol. VII. 



gated nuclei, as in the normal case, or from both conjugated 

 nuclei and male pronuclei together, as in some cases described 

 by Fol. In my experiments the eggs were impregnated under 

 normal conditions and cases of polyspermia were very rare 

 indeed. Nearly all the eggs which remained in normal sea- 

 water segmented quite normally. But I thought of the possi- 

 bility that new spermatozoa might enter the impregnated Q%g in 

 the concentrated solution. I knew that such a supposition was 

 in contradiction with all known facts, but these facts are still 

 meagre. If a polyspermia in my experiments took place, it 

 could only happen in the concentrated solution, as here the 

 increase of the number of the nuclei was observed. But I found 

 that the spermatozoa were perfectly paralyzed as soon as they 

 were brought into the concentrated solution ; that is, in the sea- 

 water to which 2 g. NaCl to lOO ccm. had been added. I 

 could show, moreover, that in this concentrated solution no 

 impregnation is effected. I brought unfertilized eggs into this 

 concentrated solution and added spermatozoa. When I brought 

 them back into normal sea-water, it took more time from that 

 moment until segmentation began than it took in normal eggs 

 and in normal sea-water from the moment of impregnation to 

 the moment of segmentation. The spermatozoa contained in 

 the concentrated salt solution became active again a few minutes 

 after being brought back into normal sea-water and then entered 

 the eggs. Polyspermia in this case could be observed, but not 

 as a rule. Most of these eggs segmented into two cells. But 

 it was astonishing how soon the spermatozoa lost their power of 

 impregnating under these circumstances. Spermatozoa which 

 had been in the concentrated solution only a few hours, when 

 brought back into normal sea-water fertilized only a thousandth 

 part, or still less, of the normal eggs ; whilst spermatozoa of the 

 same animal which had remained in normal sea- water fertilized 

 at the same time practically all the eggs of the same female. 

 When I tried to fertilize eggs in normal sea-water which had been 

 in the concentrated solution for a few hours with spermatozoa 

 that had been under the same conditions, only about one ^^g 

 in a million began to show some trace of segmentation, and as a 

 rule this segmentation remained in statu nascendi, but was not 

 accomplished. All these observations are totally different from 

 the phenomena described above. Eggs which had been fertil- 



