No. 2.] BLATTA AND DORYPHORA. 327 
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lobes ; the anterior broader and shorter is the procephalic, and 
the posterior and longer the abdomino-thoracic lobe. In both 
views of the egg (Figs. 67 and 68) a number of lines are seen 
crossing the ventral plate at right angles to the longer diam- 
eter. These lines make the plate appear segmented, and at 
first reminded me of Kowalevsky’s figure (Plate VIII., Fig. 2), 
which represents an embryo //ydrophilus in exactly the same 
stage as that which I have figured. More careful examination, 
however, convinced me that the lines were not due to segmen- 
tation, nor, in fact, depressed at all, but were the wrinkles into 
which the ventral plate was thrown, probably by a contraction 
away from the anterior pole. 
The simple method by which the ventral plate is formed is 
easily seen in a median cross-section of an egg in the stage fig- 
ured in Fig. 67 (Fig. 64). The small projection 7 is the ridge 
which separates the thick and sinking gastrular portion of the 
blastoderm (g) from the remainder of the layer. As we have 
seen, all the cells of the completed blastoderm are columnar. The 
thickened ventral plate is formed merely by the cells on the 
ventral surface of the egg lengthening in a radial direction, and 
those of the dorsum (Fig. 64 7) changing their shape so as to 
have their long axes tangentially directed. 
With further development the gastrular groove deepens and 
the ridges come close together in the median line (Fig. 70). 
The oral end of the gastrula (a) is oval, and is no longer marked 
off anteriorly by the ridge seen in Fig. 68. On each side of the 
oral widening is seen a small fold (am) between which and 
the gastrula the ventral plate cells are much thickened. This 
fold is the beginning of that portion of the amnion which sub- 
sequently envelopes the head, and the thickenings are probably 
the first traces of the brain. The egg (Fig. 70) viewed from 
the posterior end discloses some interesting facts (Fig. 69). 
The ventral plate has become pushed in at this point, and the 
thickened lip thus formed grows forward over it. This lip is 
the beginning of the caudal fold of the amnion and serosa. The 
gastrular invagination is considerably deeper at its posterior 
than at its oral end. 
The caudal fold of the amnion and serosa grows much more 
rapidly than the cephalic folds. The tail end of the ventral 
plate advances dorsally till it is one-third the length of the egg 
