244 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 



the sea-water is neutralized, or slightly acidified by the addition 

 of acid, maturation, as a rule, does not take place, although 

 otherwise it occurs with rapidity. If the eggs of the same 

 starfish are distributed among solutions which differ only in the 

 concentration of the HO ions, it will be found that the rapidity 

 with which maturation occurs increases within certain limits 

 with the concentration of the HO ions. As we shall see, it 

 is possible to evoke development in ripe starfish eggs by the 

 use of acid; hence the very method which promotes further 

 development in mature eggs prevents the immature egg from 

 maturing. 



The writer found that in different dishes the percentage 

 of matured eggs was not always the same even in similar 

 concentrations of hydroxylions. This indicated the existence 

 of another factor in addition to the concentration of the 

 hydroxylions. It soon turned out that where the eggs lay in 

 a heap maturation proceeded more slowly than where they were 

 spread out in a thin layer. This gave rise to the suspicion that 

 the supply of oxygen might be important for the maturation of 

 the eggs. Experiments in which the oxygen of the sea-water 

 was driven out by hydrogen, as well as those in which KCN had 

 been added to the sea-water, proved that in these cases the eggs 

 failed to mature in spite of the presence of the hydroxylions. 1 



2. In many annelids the entrance of the spermatozoon into 

 the egg causes first the extrusion of the polar bodies, and after- 

 ward development. The eggs of Polynoe, however, can be 

 induced to mature even in sea-water without spermatozoa by 

 adding to the sea-water some NaOH, or, better still, NH 4 OH, 

 in the proportion of about 1. 5 c.c. N/10 base to 50 c.c. of 

 sea-water. When taken out of the animal the eggs of Polynoe 

 are of irregular shape; the}' are surrounded by a thick chorion 

 and possess a large nucleus. In ordinary sea-water the chorion 



1 Loeb, "Ueber Eireifung, natiirlichen Tod und Verlangerung des Lebens 

 beim unbefruchteten Seesternei, iisw.," Pfluger's Archiv, XCIII, 59, 1902; Unter- 

 suchungen, p. 237. 



