THE BIOLOGY OF THE CELL SURFACE 



Thus, as far as we have seen, a single inducing means is 

 effective in eliciting complete development in all eggs named 

 except in the sea-urchins'. The two exposures to the solu- 

 tion of butyric acid in sea-water used on the eggs of the 

 starfish are not to be regarded as a double treatment since 

 development is initiated by one exposure if it be sufficiently 

 prolonged; in the double or intermittent exposure the effects 

 are additive. Treatment with two different means, such 

 as butyric acid and hypertonic sea-water, is unnecessary 

 for all eggs named above, except for the sea-urchin's egg 

 which does not develop normally with the original osmotic 

 method, as we have seen. 



This point is of fundamental significance since a theory 

 of experimentally induced parthenogenesis has been based 

 on the exceptional case of the sea-urchin's egg. Upon the 

 experience that the double treatment brings about good 

 development in the sea-urchin's egg a theory of general 

 application was built. And this despite the fact that for 

 all other eggs the double treatment is not necessary. But, 

 as I was able to prove, also the sea-urchin's egg can be made 

 to develop normally by a single parthenogenetic means. ^ 



Using a strong solution made up of 20, 22 or 24 parts of 

 23^^ M NaCl (or KCl) plus 80, 78 or 76 parts respectively 

 of sea-water on the eggs of Arhacia instead of the solution 

 employed by Loeb (8 parts 232 M NaCl plus 50 parts of 

 sea-water), I was able to induce the development of a high 

 per cent, of Arbacia eggs. The eggs separate beautiful 

 membranes while in any one of these solutions, but need to 

 remain in it for some time thereafter to give farther develop- 

 ment.'^ On transfer to normal sea-water after the opti- 



1 Just, ig22a. 



- It should be noted that R. S. Lillie found thai to induce complete 

 development of the starfish egg — i.e., to the larval stage — the acid 

 must act for a longer time than that sufficient to cause membrane- 



224 



