No. 2.] BLATTA AND DORYPHORA. 337 
anteriorly and posteriorly, and become united to the inner ends 
of the stomodzal and proctodzal pockets, in a manner which 
differs in no respect from what is observed in Doryphora after 
the entoderm has become definitely established. I can there- 
fore see no reason for adopting Cholodkovsky’s view as proving 
that the entoderm arises in a manner differing from that de- 
scribed above for Doryphora. As far as B#latta is concerned 
the question of the formation of the inmost germ layer must 
still be regarded as an open one. 
The embryo is hammer-shaped when the amnion and serosa 
have closed. The cephalic lobes extend around on to the lateral 
surfaces of the yolk, and each soon becomes divided into two 
lobes, a larger anterior and a smaller posterior one (Fig: 44). 
The posterior lobe is the commencement of the antenna (q/). 
In many embryos one, or, more rarely, both antennary lobes 
are temporarily bilobed (Fig. 44). This may be a slight rever- 
sion, tending to show that the antennary lobes originally gave 
rise to two pairs of appendages which were perhaps homologous 
with the two pairs of antennz in the Crustacea. The mandi- 
bles and first and second maxillz are just visible as faint out- 
growths of the ectoderm, while the more pronounced three pairs 
of thoracic legs have produced a widening of the embryo in the 
middle of its length (Fig. 44 /). 
The time required for the development described in the pre- 
ceding paragraphs is about four days. The blastoderm begins 
to contract and thicken on the seventh day from the commence- 
ment of development, and by the end of this day the area of 
proliferation is formed. Early on the eighth day the amnion 
and serosa begin to appear. They develop.rapidly, so that the 
embryo is in the slipper stage by the close of the eighth day. 
The amnion and serosa are almost or quite closed by the end 
of the ninth day. During the tenth day the mesoderm is seg- 
mented, and the cephalic and thoracic appendages begin to 
appear. The embryonal envelopes are completely formed by 
the end of the tenth day, and the embryo has assumed the 
shape of a hammer or mallet. 
