248 CLA YPOLE. [Vou. XIV. 
that surrounds the outer surface of the egg. Between the 
strands of the meshwork formed by the radiating protoplasm 
lie the numerous yolk bodies (y.), which vary much in size. 
In the central mass of protoplasm, either central or slightly to 
one side, there was usually present a rather large pear-shaped 
nucleus which proved to be the male pronucleus (m.pr.); after 
entering the egg it has assumed its permanent central position 
and is awaiting the return of the female pronucleus from the 
periphery. In many eggs there was a smaller mass of proto- 
plasm on or near the outer edge, as is shown in Fig. 30 at fz. 
In this is found the female pronucleus, the egg nucleus, for 
the first time recognizable since its disappearance before yolk 
formation began. Fig. 25 shows an enlarged view of this mass 
as seen on the periphery. Large yolk bodies (y.) are recog- 
nized imbedded in a protoplasmic mass that extends to the 
surface. At fpr. can be seen the extremely small female pro- 
nucleus returning to the centre of the egg to meet the sperm 
nucleus that is already there. P.4. shows the small and in- 
completely separated polar bodies that have been given off by 
the egg nucleus, thus completing its reduction to the female 
pronucleus. Fig. 26 shows the two polar bodies at 7.0.1 and 
p.b.2; as shown, the first polar body is again dividing, giving 
the typical number of three. Somewhere in the protoplasm 
is the female pronucleus, but not clearly outlined. The polar 
bodies never completely separate from the egg and never 
clearly protrude from the surface of the egg, but remain 
flattened down and are eventually absorbed into it. No sign 
has been found of the polar body spindles; the egg nucleus 
preserves its invisible condition in spite of the most careful 
searching, the first reappearance being in the form of the 
female pronucleus and polar bodies, as shown in Fig. 25. 
With the gradual passage of the female pronucleus towards the 
centre of the egg there is a withdrawal of the strands of proto- 
plasm in the same direction, so that the central mass gradually 
increases in size until at the beginning of cleavage it is plainly 
visible in a fresh, whole egg as a large, lighter, central spot. 
In Fig. 27 is shown a part of this mass, and in it at the centre 
the two pronuclei,— the larger, the male pronucleus, pear-shaped, 
