186 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
germinative vesicle at the end of the growth period before the dissolu- 
tion of the nuclear membrane takes place, part of it entering the retic- 
ulum and part, perhaps, the nuclear sap. While not chromatin, it 
appears to be capable of transformation into chromatin, and so may 
perhaps serve as a storehouse for material needed in the formation of 
the chromosomes. Its disappearance is by a loss of liquid substance 
or by fragmentation, or by both. 
3. Polar-Cell Formation and Fertilization.— Just before the time 
of polar-cell formation the egg is rounded and without pseudopodia; 
the germinative vesicle lies close to the periphery of the egg, its nucleo- 
lus has disappeared and its chromatin is finely divided and distributed 
along the nuclear reticulum. A decrease in the size of the germi- 
native vesicle takes place, as a comparison of Figures 45 and 46 with 
Figure 48 shows. 
Beginning at this time, or somewhat earlier, the reticulum of the 
germinative vesicle again stains intensely with nuclear dyes. ‘The 
chromatin is assembled at the nodes of the network in masses, usually 
irregular in shape and granular in appearance, which suggests the 
grouping of smaller granules into the larger mass. ‘The appearance 
in the fixed egg is well shown in Figure 48, though the germinative 
vesicle at this stage is usually not so far from the surface of the egg. 
Often the cytoplasm around the nucleus is finely granular and desti- 
tute of the vacuoles which are present in the rest of the cytoplasm. 
The history of the subsequent changes has been made out in part 
only, since certain stages could not be found. ‘The most characteristic _ 
condition found when the time of polar-cell formation approaches is 
that shown in Figures 49 and 50. The nucleus has become ovoidal, 
the long axis having a radial position. ‘The outer end of the nucleus 
is often sharply pointed, and this seems to represent a later stage than 
the more rounded condition shown in Figure 49. Almost always at 
this stage radiations are present at the outer end of the germinative 
vesicle, and the surface of the egg itself is often raised into a more or 
less conical elevation at this point. he centre of the radiations is 
always between the germinative vesicle and the surface of the egg; 
in no case were centrosomes found, nor were radiations seen at any 
other part of the nucleus. Since polar cells were apparently not 
present, it seems probable that this is a prophase of the first matura- 
tion figure, though a somewhat similar condition in Pennaria (Figs. 14, 
15) represents a stage after the first polar cell has been formed. ‘There 
is no evidence upon which to determine whether there is a division 
of this aster to form two centres, or whether the spindle centres arise 
OS ees. 
