40 CLEAVAGE II 



where they segment normally 1 and develop into swimming 

 larvae. 



The larvae produced by this improved method of artificial 

 parthenogenesis may be reared through the metamorphosis 

 and reach the adult condition. It should not be forgotten 

 that the credit of first accomplishing this belongs to Yves 

 Delage (who used, however, a different method), and that at 

 a time when the means now employed at Plymouth for 

 rearing larvae had not come into use. The individual first 

 successfully raised by Delage was a male, with ripe gene- 

 rative products. 



The success of Loeb's experiments naturally gave an impetus 

 to the inquiry into this problem, and artificial partheno- 

 genesis has been induced in the eggs of many animals, by 

 many methods in the hands of various investigators. 



Thus, Delage used for Sea-urchins (Strongylocentrotus) acids 

 and alkalis alternately, for Asterias, carbon dioxide : Lefevre 

 has employed acids for Thalassema, Loeb, saponin for Polynoe. 

 Osmotic pressure (hypertonic solutions) has given good results 

 with Mactra (Kostanecki), Glmetopterus (Loeb, Mead), Amphi- 

 trite (Scott), Nereis (Fischer), Ophelia (Bullot). Greeley has 

 found cold sufficient, Lillie heat for Asterias, while Mathews 

 used merely mechanical agitation for the same form. Lastly, 

 in Vertebrates, Bataillon found that while hypertonic solu- 

 tions would cause the eggs of Petromyzon and Rana to pass 

 through only a few of the cleavage divisions, the eggs of the 

 latter might be stimulated not only to segment but to de- 

 velop by being punctured with a fine needle. From the 

 punctured egg a perivitelline fluid was exuded, in it a grey 

 crescent appeared at the normal time, the eggs segmented 

 and a few of the larvae produced lived almost to the meta- 

 morphosis. 



Though the very diversity of the means mechanical, 

 physical, chemical by which artificial parthenogenesis may 



1 That is, the first three furrows are meridional, meridional, and 

 equatorial. We are not told whether in the next division the charac- 

 teristic mesomeres, macromeres, and micrometres are produced. 



