34 THE DEVELOPMENT OF THE CHICK 
Thus at each end of the spindle there are eight dyads. Those at 
the outer end then enter a little bud of protoplasm projecting 
above the surface of the germinal disc, and this bud with the 
dyads is cut off as the first polar body, which hes in a depression 
of the germinal dise beneath the vitelline membrane (Fig. 11). 
Right dyads, therefore, remain within the germinal disc. 
A second maturation spindle is then formed almost imme- 
diately, apparently without the intervention of a resting stage 
of the nucleus, and takes a radial position similar to that occupied 
by the first, with the dyads forming an equatorial plate (Pig. 11). 
Fie. 11. Second maturation spindle and first polar body of the pigeon’s 
egg; a combination of two sections. 8.15 p.m. x 2000. (After Harper.) 
m. Sp. 2, Second maturation spindle. p. b. 1, First polar body. v. M., 
Vitelline membrane. 
ach dyad then divides along the preformed plane of division, 
and the daughter-chromosomes diverge towards opposite poles 
of the spindle. The outer end of the second maturation spindle 
then enters a superficial bud of the protoplasm of the germinal 
dise similar to that of the first maturation spindle; and this bud 
together with the contained chromosomes becomes cut off as the 
second polar body. 
The result of these processes of maturation is the formation 
of three cells, viz., the two polar bodies and the mature egg. 
The polar bodies are relatively very minute and soon degenerate 
completely. 
After the formation of the second polar body there remain 
in the egg eight chromosomes, each of which represents one 
> 
quarter of an original tetrad. These form a small resting nucleus 
known as the egg-nucleus or female pronucleus. It is many 
times smaller than the original germinal vesicle (Fig. 12), and 
