No.2.) BLATTA AND DORYPHORA. 355 
head of the larva, and (4) an increase in the length of all the 
appendages except the antennz. The shortening of the embryo 
stops as soon as its tail reaches the caudal pole of the egg, the 
lateral growth of the body continues, and we reach the stage 
figured (Fig. 74). The yolk is not yet covered by the dorsad 
growing walls of the embryo. The head is distinctly marked 
off from the thorax, the wide-spread mouth parts of Fig. 72 have 
converged, and are assuming the relations which they bear to 
one another in the larva. The ventral nerve chord has devel- 
oped considerably, and it is now possible to recognize near the 
centre of each ganglion the mass of “ Punktsubstanz”’ definitely 
marked off from the cellular portion and united with the corre- 
sponding mass of its fellow-ganglion by two-cross commissures. 
Figure 75 represents.the larva ready to hatch. The dorsal 
body wall has closed, the six ocelli have become pigmented, 
the cuticle has developed spines, the meso- and metathoracic 
and first abdominal segments have each developed a short, 
sharp, black spine in a line with the abdominal spiracles. 
These spines are used by the larva in rupturing the chorion, 
the vitelline membrane, and the various cuticles which it has 
shed before reaching this stage. The movements of the hatch- 
ing insect at first produce a rent in the chorion extending from 
the first to the third spine, by further struggling the two rents 
from opposite sides are made to meet over the head, and the 
insect emerges from between the two lips thus formed. The 
embryonic development requires about six days. 
Before passing on to a description of the internal changes of 
Doryphora and Blatta, it is necessary to consider the fate of the 
embryonic membranes of the former insect. This is very differ- 
ent from what was observed in Blatta. The serosa, instead of 
rupturing when the amnion ruptures, separates from it and also 
from the entire surface of the yolk, and forms a third egg enve- 
lope, beneath the vitelline membrane, to which it applies itself. 
It remains clearly recognizable by its large and deeply staining 
nuclei till the insect is almost ready to hatch (Fig. 86 s7), when 
it disappears, probably by absorption. The fate of the amnion 
is peculiar. On rupturing, its two ventrally bent folds turn back 
and become in part applied to the yolk. A few of its cells are 
loosened from the bulk of the membrane, and are often seen 
sticking to the serosa at different points. They are probably 
