314 WHEELER. [ VoL. IE. 
been produced by reagents, as these eggs were hardened in 
picrosulphuric acid or simple alcohol, which in younger and 
older eggs preserve the karyokinetic figures of the cleavage 
nucleus and its immediate descendants with great clearness. 
The nuclei of the small syncytia spread apart evenly over the 
surface of the egg, which now presents the appearance of Fig. 
37. The pseudopodia of the amceboid cytoplasmic masses run 
together to form a net. The egg is now in the blastema stage 
of Patten (38). The cells at the surface are being continually 
reinforced by cells migrating from the yolk. Ever since the 
first division of the cleavage nucleus the nuclei have undergone 
a gradual and steady diminution in size, and this progresses till 
the formation of the blastoderm which takes place by the 
division of the blastema cells. In this stage the yolk is covered 
with a layer of protoplasm, imperfectly divided into small cells, 
each containing a lenticular nucleus, which in turn contains two 
very deeply stainable nucleoli (Fig. 33). Fig. 27 is a trans- 
verse section through the front of an egg in the blastoderm 
stage. All the protoplasm at the surface of the egg is carried 
there by the migrating cells or formed from the surface yolk 
through their influence, as the Kezmhaut, so highly developed 
in Doryphora, as will be seen further on, is undeveloped on the 
ventral, lateral, and all but a very small portion of the dorsal 
surface of the egg of Blatta germantca. 
All the nuclet, formerly in the yolk, probably rise to the sur- 
face to form the blastema and reinforce it in its formation of 
the blastoderm. Before the blastoderm is completed, cells sep- 
arate from it and pass inwards to form the yolk cells, or 
vitellophags. The following are my reasons for believing that 
all the products of the cleavage nucleus go to the surface. The 
cleavage nucleus cells have large pale nuclei and distinctly 
amoebiform cytoplasm, like those in the yolk of Figs. 25 and 26. 
Subsequently none of these nuclei are to be found in the yolk, 
but in their stead occur at greater or lesser distances from the 
ventral and lateral faces small deeply stainable nuclei of exactly 
the same size as the blastoderm nuclei, not surrounded with 
amoebiform cytoplasm, but apparently melting their way through 
the yolk, often in the middle of a dense yolk body, and, above all, 
exhibiting the same intimate structure as the blastoderm nuclei 
(Fig. 28). When treated with picrosulphuric acid, these centrip- 
