ORGANIZATION AND CELL-LINEAGE OF ASCIDIAN EGG. 17 
of indirect cell division. Inasmuch as some of the cleav ages also throw light on 
this problem, its further consideration will be postponed to the section which deals 
with the first cleavage. 
9. Movements of Spindle and of Nuclear Plasm ; formation of Polar Bodies. 
In Cynthia the first maturation spindle and the surrounding nuclear plasm re- 
main indefinitely in the condition shown in figures 77 and 78 unless the egg be ferti- 
lized. In Czoza the stage at which the maturation processes come to rest is a little 
more advanced than in Cynthia, as is shown in figure 172; the peripheral layer of 
protoplasm is here collected over the lower hemisphere of the egg, and the nuclear 
_ plasm which has escaped from the germinal vesicle forms a layer over the entire 
upper hemisphere. Unfertilized eggs may remain in this condition for at least 
three or four hours and still be capable of fertilization and normal development; 
. but if they remain unfertilized for ten or twelve hours the nuclear plasm spreads 
NIRS. 
E 
Fie. м күнме; partita which had Jain twelve hours without being fertilized. 
The a Giger ng m p. габ lies in t he position in which it was first formed; the peripheral layer 
of yellow protoplasm ( ا‎ лен distributed over the "RE but the in РЕТ авт 
spread throughout the up into irregular masses (compare with figs. 77 and 78 
showing unfertilized eggs ы айыру соп 
Fre. IL. ей tion of an entire re egg o f Cynthia partita, showing small spindles at oppo- 
site poles (1. ced inia which are possi AL "eg maturation estilos, though more probably one of these 
E precociousl y 4 
through. the substance of the yolk in irregular masses (cf. text fig. I), and the eggs 
thereafter are not capable of normal fertilization. The maturation and further 
development of the egg are finally and forever halted in this early stage unless 
the egg be fertilized. Ав soon as a spermatozoon enters the egg active move- 
ments of the protoplasm begin and a localization of different öoplasmic materials 
occurs, | which will be described later; at the same time the first maturation spindle 
moves to the animal pole and is turned from a paratangential to a nearly radial 
position. The daughter chromosomes then separate and the first polar body is 
extruded (figs. 66-68 and 79-82). 
The second maturation spindle is smaller than the first, as Castle has shown, 
a like the. first, is paratangential in position in early stages and only later 
becomes radia radial. - The second polar body is extruded close to or immediately under 
3 JOURN. A. ¥ & PHILA. VOL. ХІП. 
