112 E. E. JUST. 



outset the fixation by the spermatozoon of the escaping fertilizin. 

 This takes place in Platynereis almost instantaneously ^ee page 

 93) but brief though this phase may be it cannot be omitted. 



The experiments with Nereis sperm and agents of artificial 

 parthenogenesis demand explanation. Eggs such as those of 

 echinids used in cross fertilization (Loeb, Tennent, Baltzer, 

 Herbst, etc.) or in artificial parthenogenesis when subjected to 

 treatment are so subjected with their substances intact. They 

 are normally shed in sea-water for insemination and the sea-water 

 does not for some time destroy their fertilizing power. Platy- 

 nereis eggs when subjected in sea-water to foreign sperm or to 

 various agents have lost something through the action of sea- 

 water. This very "something" is necessary for artificial par- 

 thenogenesis and, moreover, as shown above (for Nereis also) 

 must be present in greater quantity than necessary for fertiliza- 

 tion. I am emboldened further to suggest that eggs normally 

 inseminated in the ovocyte stage yield to parthenogenetic agents 

 only with difficulty because they lose fertilizin at the impact of 

 the first stimulus — chemical treatment, shock, etc. Sperm 

 alone, in most cases, are strong enough by fixation of the fertilizin 

 to carry such eggs through their dual phase — maturation and 

 fertilization. Whether by sperm, then, or by artificial agents, 

 the initiation of development is fundamentally the same.^ The 

 egg plays the leading r61e; it needs but to have its fertilizin ac- 

 tivated in order to develop. 



The observations on Platynereis were rendered less difficult 



because of the study of the maturation and fertilization in Nereis. 



For this study I was fortunate to be able to supplement my own 



slides with two series lent me by Professor F. R. Lillie. It is a 



genuine pleasure here to acknowledge my further indebtedness to 



him for his many suggestions and for his stimulating interest in the 



Platynereis studies begun at his suggestion and under his direction. 



Marine Biological Laboratory, • 

 Wood's Hole, Mass. 



1 I think that Martin Jacoby's experiments support this view. He found {Bio- 

 chem. Zeit., 26, 333-335) that serum from rabbits into which eggs had been injected 

 showed an increased power to stimulate parthenogenetic development of the eggs. 

 He also found {ibid., pp. 336-343) that an enzyme which may be extracted from 

 sperm and from eggs after sperm penetration may be got from parthenogenetic 

 eggs. 



