No. 2.] BLATTA AND DORYPHORA. 353 
diagrammatic, being drawn from a number of different embryos, 
each of which contributed some of the details in a clearer and 
more pronounced manner. The mouth (9) and anus (a), both 
triangular depressions, have become clearly established. The 
former has in front of it a heart-shaped prominence, the bilobed 
labrum. The lateral half of the head presents some interesting 
facts, first elucidated in Patten’s paper on the eyes of Aczlius 
(39). Each half of the head is divided by longitudinal constric- 
tions into three parallel rounded ridges, each of which is further 
divided by two transverse depressions into three subquadran- 
gular thickenings. The three inner (61, 2°, 4°) on each side, rep- 
resenting the three segments of the brain, are directly continuous 
with the ventral ganglion chain, extending to the protodzum. 
The row of prominences (ag1, og?, og*) on the outer side of the 
three brain segments are the optic ganglion, the further three 
(0p', of”, of®), somewhat indistinctly seen because situated on 
the very edge of the head, are the divisions of the optic plate, 
each of which, in Acz/zus, according to Patten, bears a pair of 
ocelli. The only appendages of the head proper in this stage 
are the antennz (a¢), which are directed backwards, and the 
heart-shaped labrum. The head also presents three pairs of 
small invaginations somewhat less distinct than in the figure 
(¢1, 22, ¢3). These he near the longitudinal constriction, sepa- 
rating the brain thickenings from the thickenings of the optic 
ganglion. This is best seen in the third segment, where the 
invaginations lie at the bases of the antennz. Following the 
third segment of the brain is distinctly seen in some embryos 
a short segment inserted between the antennary and mandibular 
segments. Its short ganglionic swellings (g/‘) are far apart, 
and connected by a broad commissure. This somite may also 
have a pair of small invaginations, but I have been unable to 
find them. Hereupon follow the mandibular, and the first and 
second maxillary segments, each with a pair of invaginations. 
Those of the second maxillary segment are concealed behind 
the bases of the elongated appendages, but are readily seen in 
sections. 
The three broad thoracic segments are provided with the 
three pairs of legs, all of which are of the same length. The 
division into femur, tibia, and tarsus is indistinctly marked. , In 
none of the preceding stages have I observed what is so prom- 
