140 ARTIFICIAL PARTHENOGENESIS AND 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 HCl (in 4 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 HCl, and, as usual, 
these all went to pieces. However, those eggs which had been 
up to three minutes in N/12 HCl 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 
HC] solution (and which had formed no membranes after trans- 
ference to normal sea-water), and even after five minutes’ 
exposure to the N/12 HCl 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 HCl 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 
