200 MEAD. fVOL. Ah. 
While these phenomena, directly connected with the develop- 
ment of the male pronucleus and amphiaster, have been going 
on, the first maturation-amphiaster, whose activity was resumed 
upon the entrance of the spermatozoon, has brought about an 
apparently independent series of changes in another part of the 
egg resulting in the formation of the polar globules. 
Beginning with the formation of the polar globules, the living 
ege undergoes a constant series of form changes, these being 
most pronounced in eggs taken from worms which have been 
but a short time (one or two days) in the aquarium. While the 
first polar globule is being formed, the egg, at first spherical, 
becomes distinctly flattened at the animal pole. This reminds 
one of the flattening of the adjacent surfaces of the cleavage- 
blastomeres which occurs shortly after cell-division. 
The egg resumes its spherical form, but, after the extrusion 
of the second polar globule, becomes pear-shaped, the smaller 
end at the animal pole. It again assumes for a short time 
the form of a sphere. A protuberance then appears upon the 
vegetative hemisphere. The successive stages in the devel- 
opment of this protuberance — yo/k-lobe — are uniformly syn- 
chronous with the various phases of the first cleavage-mitosis.! 
The lobe first becomes noticeable during the.early metaphase 
of the spindle, and reaches the height of its development during 
the telophase. Meanwhile, the first cleavage-furrow cuts the 
egg into two unequal cells and the lobe remains attached to the 
larger one, into which it is later resorbed. These phenomena 
are of especia] interest in connection with certain experiments 
which I have made upon unfertilized eggs. 
Soon after the maturation-spindle resumes its activity the 
nine chromosomes divide and the daughter-chromosomes migrate 
toward the two poles of the spindle, while the double centro- 
somes at the inner end of the spindle move apart and a small 
central spindle is formed between them (Figs. 14-20). The 
centrosphere fades away and the rays diverge directly from the 
two centres, as was the case in the evolution of the sperm- 
in the behavior of both; but, notwithstanding these variations, the axis of the 
amphiaster is in every case at right angles to the egg-axis. 
1 The same is true of the yolk-lobe in mollusks; cf Crampton. 
