ARTIFICIAL PARTHENOGENESIS AND EKRTILISATION. 485 



5, Exposure to weak HOI iu sea water, and subsequent 

 restoration to pure sea water. Asterias (Loeb, Delage). 



6. Continuous exposure to a solution of a specific chemical 

 substance at the same osmotic pressure as normal sea water. 



Potassium Chloride. Cha3topterus (Loeb). 



Calcium Chloride. Amphitrite (Fischer). 



The Ions of potassium and calcium are said to be specific 

 for these forms respectively.-^ 



With regard to the influence of the state of maturation, 

 Delage gives results to show that in Asterias glacial is, 

 when the eggs are placed in sea water to which is added an 

 equal quantity of a solution of HCl, raising the molecular 

 concentrations of the mixture to 0*660, different results are 

 got according to the stage of maturation. Among the eggs 

 placed in the liquid before maturation, 20 per cent, of 

 blastultB were got, at the appearance of the first polar 

 body 95 per cent., and after the appearance of the second 

 polar body 5 per cent., while none of the controls showed 

 any normal segmentation. 



From all this it seems that changes in the osmotic 

 pressure between the egg and its surrounding medium, and 

 mechanical agitation, are the chief agents so far as yet 



1 Delage (' Conipt. lleiuius de I'Acad. des Sciencej;,' October IStliaiid 20tli, 

 1902) announces tiiat lie has found an agent wliicli is as certain and efTective 

 as the spermatozoon, in producing development to advanced h-irval stages, in 

 Asterias. It is sea water aerated by carbonic acid gas, and at the same osmotic 

 pressure as ordinary sea water (or lower ?). When the eggs, at what he 

 calls the "critical stage" — i.e. when the nuclear membrane of the germinal 

 vesicle is dissolved, up to the expulsion of the first polar body — are placed in 

 this, and after one hour transferred to pure sea water, practically all the eggs 

 develop. His view is, that the maturation is arrested temporarily, and on 

 restoration to pure sea water, the carbonic acid gas is quickly eliminated and 

 division proceeds ; but it is not partial, as in the polar mitoses, but complete, 

 and goes on to the formation of the normal larval forms. The result is not 

 obtained at a stage after the polar bodies are extruded and the ovum has again 

 come to rest, nor is it a|)plicable in sea-urchin, iu which the maturation is 

 over before the ova are shed. His theory as to the action of the gas is, that 

 it is a temporary poison which arrests maturation completely, and is quickly 

 removed afterwards without altering the characters of the protoplasm. 



