140 ARTIFICIAL PARTHENOGENESIS AJND FERTILIZATION 



chiefly by the relative velocity of their absorption by the cell, 

 and analogy urges a similar supposition in the case of the acids. 



The direct proof is as follows. If it is true that the weak 

 monobasic fatty acids are more effective for the purpose of 

 membrane formation than the strong mineral acids, for the 

 very reason that the former are more quickly absorbed by the 

 egg, it would be expected that the fatty acids are more injurious 

 to the egg and kill it more quickly than the mineral acids; 

 for in order to kill the egg the acids must enter it. Now this 

 can be very easily tested by placing the eggs of the same female 

 in different acids (diluted with \ m NaCl solution), and deter- 

 mining how long they must remain in the various acids to lose 

 their faculty of being fertilized and of developing. 



Unfertilized sea-urchin eggs were therefore put into a N/12 

 solution of HC1 (in \ m NaCl solution), and transferred from 

 this to normal sea-water every half-minute, when a sample of 

 them was fertilized with sperm. Only a few had formed 

 membranes as a result of treatment with HC1, and, as usual, 

 these all went to pieces. However, those eggs which had been 

 up to three minutes in N/12 HC1 and had formed no membranes 

 formed them upon the addition of sperm and developed to 

 swimming larvae. The addition of sperm caused development 

 in 20 per cent of the eggs which had been four minutes in the 

 HC1 solution (and which had formed no membranes after trans- 

 ference to normal sea- water), and even after five minutes' 

 exposure to the N/12 HC1 solution, 10 per cent of the eggs could 

 still be fertilized and caused to develop by sperm. It is scarcely 

 necessary to mention that weaker concentrations of HC1 were 

 much less injurious. 



Before we turn to the experiments upon the toxicity of the 

 monobasic fatty acids, I must once again remind the reader 

 that the eggs form no membrane so long as they are in the lower 

 fatty acids, but only after they have been transferred to the 

 (weakly alkaline) sea-water; and moreover that the membrane 



