XXIV 



CONDITIONS FOR THE MATURATION OF THE EGG 



1. Before we discuss experiments upon artificial partheno- 

 genesis in other forms besides sea-urchins, we must examine 

 the phenomena presented by the ripening egg. We mentioned 

 in the introduction that development proper, i.e., the segmenta- 

 tion of the egg, must be preceded by its "maturation." This 

 is a process which consists morphologically in the reduction of 

 the nucleus by two divisions and the extrusion from the egg of 

 parts of the nucleus as polar bodies. This process of matura- 

 tion shows a connection with the process of fertilization in so 

 far as in many forms maturation is initiated by the entry of a 

 spermatozoon into the egg. In other forms maturation pro- 

 ceeds spontaneously either in the ovary (sea-urchin) or after the 

 eggs have been shed into sea-water (starfish), and until this 

 happens the spermatozoon does not or cannot enter the egg. 

 Whereas one finds that the majority or very many of the eggs 

 are ripe in the ovary of the sea-urchin, this is seldom the case 

 with the starfish; still the eggs of the starfish usually mature 

 quickly on being put into sea-water. When the eggs of the star- 

 fish are removed from the ovary, they possess as a rule large, 

 conspicuous nuclei. Maturation consists in the reduction of 

 the size of the nucleus by a double division and the extrusion 

 of the polar bodies. The time that elapses before these processes 

 take place in sea-water differs for the eggs of different starfish. 

 This probably depends on the fact that the eggs of different 

 females are not all in the same condition of ripeness. Experi- 

 ments which I performed a few years ago upon the maturation 

 of the eggs of the starfish (Asterias forbesii) in sea-water indi- 

 cated that maturation is accelerated by two of the substances 

 present in sea-water, viz., the hydroxylions and the oxygen. If 



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