194 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 



It was observed in the experiments with the blood of 

 mammals that, just as with the Dendrostoma blood, it was not 

 the eggs of every sea-urchin that would respond, but only the 

 eggs of about 10 per cent of the females. I am inclined to 

 attribute this to differences in the permeability of the eggs of 

 different females. In order that the blood may cause membrane 

 formation, it is necessary for its effective constituent to diffuse 

 into the egg. It seems then that the necessary degree of per- 

 meability will not be found in the eggs of every female, but 

 only in those of a certain percentage. Moreover, the blood of 

 mammals is less effective than that of Dendrostoma. Whereas 

 the latter produces membrane formation when diluted 100 to 

 1,000 times, the former is effective only in 2 to 10 times dilution. 1 

 The experiments succeed best when the eggs are taken fresh 

 from the ovary. 



2. The fact that not the eggs of every female reacted with 

 foreign blood made it necessary to find methods of sensitizing 

 the eggs to the effects of foreign blood. Various methods were 

 tried. A rise in temperature seemed at first promising. In the 

 following experiment the eggs of a female were used of which 

 about 3 per cent formed membranes with ox serum at room 

 temperature. 



The eggs of this female were put in a beaker with sea-water; 

 the ox serum was put in a second beaker, and both were heated 

 slowly in a water bath. At certain temperatures 0.5 c.c. of 

 sea-water + eggs and 0.5 c.c. of serum were mixed in a watch 

 glass, and the percentage of eggs that formed membranes 

 was estimated. The result of one such experiment is given in 

 Table XXXVI. 



1 T. B. Robertson has recently found that ox serum acts best in a dilution of 

 1 : 16 with sea-water. He even obtained results with a greater dilution (Robertson, 

 Archiv f. Entwicklungsmechanik, XXXV, 70, 1912). Wasteneys and I did not 

 notice such an effect of dilution on the egg of Arbacia, where the results agreed 

 with the writer's former observations on S. purpuratus. Robertson ascribes 

 the beneficial effect of dilution to the presence of an inhibiting factor in the 

 serum. 



