598 The American Naturalist. [July, 
the early stages of cleavage and, asa rule, in the later stages and in 
the blastula, but in the later stages of cleavage and in the blastula 
there are often cells that contain eight. | 
In the maturation of the egg four chromosomes come out of the net 
work of the resting nucleus and eventually four go into the first polar 
body and two into the second. This is brought about as follows: The : 
four very long chromosome loops shorten and divide lengthwise into 3 
four cleft rods. When these come to the equatorial region of the first 
maturation spindle they have again closed together so as to form four : 
simple rods. These separate in pairs and move towards the poles of 
the spindle without presenting any true mitotic division. The first 
maturation division is, therefore, a reducing division. Yet the first 
polar body receives four chromosomes, since the pair that approaches 
that pole divides, as if opening out where previously split, and thus 
four rods are formed. The same takes place atthe inner pole and four 
are left for the second maturation spindle. In the second polar body 
two chromosomes enter by moving away from the other two left in the 
egg. Asit cannot be determined whether the pair entering the second 
polar body are two halves of one of original ones or halves of two 
original ones it is not certain whether the second maturation division 
is a reducing or an equating division, 
Though the chromosomes are usually short rods or elongated gran- 
ules during the maturation division, there are many eggs in which — 
they appear as long, bent or horse-shoe shaped rods. 
Some exceptions to the above account must be emphasized as show- 
ing the inconstancy of number of chromosomes resulting from lack of © 
synchrony between chromosomal divisions and other phenomena of the 
cell. 
Thus in some cases the first polar body has but two chromosomes, — 
since the preceding division of chromosomes is left out. In others — 
eight chromosomes are found at the equator of the first polar spindle, © 
formed by a precocious division of the four chromosomes ! 3 
Fertilization takes place normally just after the eggs are laid and 
the sperm enters, while the first maturation spindle is still patent. In _ 
abnormal cases fertilization may take place inside the parent which is — 
hermaphrodite and may ripen sperms and eggs simultaneously. Such 
cases, however, lead to abnormal cleavages and even to fusion of sepa- _ 
rate eggs, and seem due to some pathological state of the egg. = 
When the sperm enters the egg radiations are formed behind it, and 
later in front of it, so that the middle piece of the sperm may be re- 
PP a tee 
