{ 
Vpn 
OM-- mpl ’ m.pr. 
— 
hg ) 
126 Darwin, and after Darwin. 
and result in the formation of many different kinds of 
cells, in the order required for constructing the multi- 
cellular organism to which the whole series of processes 
eventually give rise. We have now to consider these 
processes serzaziin. 
First of all the nucleus discharges its polar bodics, 
as previously mentioned, and in the manner here 
depicted on the previous page. (Fig. 33.) It will be 
observed that the nucleus of the ovum, or the germinal 
Nad 
HL Te 
PT 
Fic. 34.—Fertilization of the ovum of an echinoderm. (From Quazn’s 
Anatomy, after Selenka.) S, spermatozodn ; m gr., male pronucleus; . 
J pr., female pronucleus. 1 to 4 correspond to D to G in the next 
figure. 
vesicle as it is called, gets rid first of one and after- 
wards of the other polar body by an “indirect,” or 
karyokinetic, process of division. (Fig. 33.) Extrusion 
of these bodies from the ovum (or it may be only from 
the nucleus) having been accomplished, what remains 
of the nucleus retires from the circumference of the ovum, 
and is called the female pronucleus. (Fig. 33. fpz.) 
The ovum is now ready for fertilization. A similar 
emission of nuclear substance is said by some good 
