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.! 
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,OH, 
in the proportion of about 1.5 c.c. N/10 base to 50 e.c. of 
sea-water. When taken out of the animal the eggs of Polynoe 
are of irregular shape; they are surrounded by a thick chorion 
and possess a large nucleus. In ordinary sea-water the chorion 
i Loeb, ‘‘Ueber Eireifung, natiirlichen Tod und Verlangerung des Lebens 
beim unbefruchteten Seesternei, usw.,’’ Pfliiger’s Archiv, XCIII, 59, 1902; Unter- 
suchungen, p. 237. 
