174 COMPAPvATIVE PHYSIOLOGY 



of considerations converge to reinforce this conclusion, Lyon 

 and Schackell have shown that eggs become more permeable 

 to dyes as the result of fertihsation. Harvey (1910) has not 

 only confirmed this, but shown by intravitam staining with 

 neutral red a temporary increase at fertilisation of the per- 

 meability of the egg to alkalies. Again, Lyon (1909) found 

 that fertilised eggs of sea-urchins, three minutes after insemina- 

 tion, liberate about double as much oxygen from hydrogen 

 peroxide as do unfertilised eggs, a fact most readily expHcable 

 on the assumption that the intracellular catalases are more 

 accessible to the peroxide in the former case. Thus normal 

 fertilisation may be regarded as a phenomenon of which one 

 result is that water tends to be withdrawn from the cell ; we 

 can imitate this process either by withdrawing water from the 

 cell (osmotic activation), or by changing the surface properties 

 of the cell-surface so as to increase its permeability, as appears 

 to be the effect of butyric acid and of cytolytic reagents. 

 According to Carter (1924) the formation of a fertiUsation- 

 membrane is not an essential feature of this change. 



The surface change which accompanies fertilisation can 

 be induced in quite a number of ways. The eggs of the poly- 

 chaete Nereis (which provides more accessible material for 

 workers in this country than sea-urchins, as it spawns all 

 through the summer) can be made to segment (i) by osmotic 

 activation (Fischer), (2) by exposure for a suitable period to 

 a temperature of 35° -36° C ; (3) by standing them for ten 

 minutes in the sea-water exudate of Echinoderm eggs or 

 Echinarachnus lipolysin. Potassium cyanide, radium emana- 

 tions, fat-solvents, alcohol, distilled water, saponins, bile- 

 salts, sera, mechanical injury — the method which can be used 

 for fertilisation of frog's eggs — have all been employed 

 successfully as substitutes for the fertilising action of the sperm. 

 It is not profitable in the limited space at our disposal to select 

 further instances from an extensive literature deahng with 

 artificial parthenogenesis in representatives of Echinoderms, 

 Polychastes, Molluscs, Arthropods, Fishes, and Amphibia. 

 In general we may say that all these agencies have in common 

 the property of producing cytolysis at the surface of the egg. 



