PAR THENOGENESIS 



the phenomenon of fertilization. The problem seemed to 

 be especially easy, since the double treatment — and, there- 

 fore, the factors in the explanation — in these experiments on 

 inducing parthenogenesis, appears to have parallels in the 

 two phases in fertilization, the external and the internal 

 phase. I shortly review these here. 



All eggs respond to insemination, as was pointed out, 

 by some kind of surface or ectoplasmic changes which pro- 

 duce in some cases very striking results, as the separation of 

 the vitelline membrane in sea-urchins' eggs or the extrusion 

 of the superficially located material in eggs of the genus 

 Nereis which sets as a jelly in the sea-water. Underlying 

 these changes is always a disintegration of the superficial 

 cytoplasm upon which follows normally a rapid reconstitu- 

 tion of the surface. This is the so-called first or external 

 phase of the fertilization-process. 



Once within the egg, the nucleus of the spermatozoon 

 moves toward the egg-nucleus. Both division-centres arise 

 near one or the other of the germ-nuclei or one centre 

 near the egg- and the other near the sperm-nucleus. 

 The mitotic spindle is established and first cleavage is 

 initiated. These phenomena constitute the so-called second 

 or internal phase of the fertilization-process. 



With respect to these two phases, it is true that experi- 

 mental parthenogenesis in the sea-urchin egg initiated by 

 butyric acid and hypertonic sea-water resembles the fer- 

 tilization-process inasmuch as the acid calls forth mem- 

 brane-separation and the hypertonic sea-water initiates the 

 formation of an amphiastral mitotic figure. Therefore, 

 the superficial cytolysis corrective factor theory though it 

 can not be upheld as explanation of experimental partheno- 

 genesis, may, one might think, nevertheless explain fertili- 

 zation. Attempting such an explanation, Loeb says that 

 the "fertilization by the spermatozoon perhaps depended 

 not upon a single chemical agent, but upon a combination 



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