142 ARTIFICIAL PARTHENOGENESIS [CH. 



If the solutions are used in the way described, no normal 

 development takes place unless both solutions are used; 

 under certain circumstances, however, it is possible to 

 obtain development by treatment with either acid or hypo- 

 tonic solution alone, although with the concentrations and 

 length of exposure mentioned both are necessary. This fact 

 naturally leads to the question What are the effects of the 

 two solutions, and how do they co-operate to bring about 

 development? In the earlier experiments on artificial 

 parthenogenesis no fertilisation membrane was formed, but 

 experiments designed to elucidate the nature of this mem- 

 brane have led the way to an analysis of the factors which 

 initiate development. When the eggs have been treated 

 with butyric acid and returned to sea-water they immedi- 

 ately begin to form a fertilisation membrane, but if they 

 are left in sea-water after the membrane is formed, although 

 a mitotic spindle may be produced, followed by division of 

 the nucleus, they then begin to disintegrate. Droplets of 

 protoplasm begin to be exuded, especially in the region in 

 which the first segmentation furrow is forming, and gradu- 

 ally the protoplasm breaks up into fragments, the disin- 

 tegration beginning at the surface and gradually extending 

 through the egg. At a lower temperature the disintegration 

 or cytolysis proceeds more slowly, and the egg may divide 

 into two or more blastomeres before cytolysis has progressed 

 so far as to destroy it. It appears, therefore, that the same 

 treatment which brings about membrane formation also 

 leads to cytolysis, and this conclusion has been confirmed 

 by numerous observations on the effects of various sub- 

 stances on the egg. All these experiments point to the con- 

 clusion that cytolytic agents of any kind, if used in the 

 proper concentration, tend to bring about the production 

 of a fertilisation membrane, and to initiate cell-division, 



