628 Gro. W. TANNREUTHER, 
. Development of the ova of the parthenogenetic andl 
presexual generations. 
After the formation of the polar body the nucleus passes to 
the center of the egg. The prophase of the first cleavage nucleus — 
is shown in Pl. 53, Fig. 127—128. The polar body is visible near £ 
the periphery as a dark chromatin mass. The spindle of the first 
cleavage is well organized (Fig. 129). The cytoplasm is vacuolated. 
After the first cleavage, the daughter nuclei pass nearer the peri- 
phery. All the subsequent divisions of the cleavage nuclei occur 
near the surface of the egg. The position of the cleavage nuclei 
after the first and second cleavages is shown in Pl. 50, Fig. 34—35. 
After the third cleavage (Fig. 36—37), the egg becomes more 
elliptical and the nuclei take a position nearer the surface of the 
egg (Fig. 38—39). The nuclei divide simultaneously and pass through 
a short resting stage after each cleavage. The nuclei have a distinct 
nuclear membrane (Fig. 38). As the egg elongates the cleavage 
nuclei fuse with the peripheral cytoplasm of the egg. The peripheral 
cytoplasm separates into parts corresponding to the cleavage nuclei 
(Fig. 40). 
The cleavage nuclei that do not pass to the periphery in the 
formation of the blastoderm divide once or twice mitotically and 
prepare the yolk for assimilation. The yolk originates as granules 
within the cytoplasm. These granules increase in size and form 
spherical-like masses with yolk nuclei in the center (Fig. 41). 
The blastoderm forms a continuous epithelial band around the 
ege except at the extreme posterior end, where the so-called blasto- 
phore is formed. On either side of this opening the blastoderm 
begins to invaginate by a rapid proliferation of the blastoderm 
nuclei (Fig. 41—42). 
The nuclei of the entire blastoderm may divide once or twice 
before invagination begins. Thus the blastoderm may become one 
or several cells thick (Fig. 42). 
The blastoderm now has reached its maximum growth and the 
part which does not invaginate becomes more reticular and forms 
the serosa. 
| 
The development of the ova in the parthenogenetic generations 
and the presexual or last parthenogenetic is the same. The only 
difference is that the presexual individuals contain but few ova and 
