IOWA ACADEMY OF SCIENCE 
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There next appears at the dorsal, anterior end, a thickening of the cell layer, 
by addition of new cells beneath the surface layer (PL I, fig. 5-p). This is the 
beginning of the primitive band. At the same time the blastoderm begins to 
fold in above this point, and as the cells underneath increase in number the 
fold pushes them downward and backward (PL I, figs. 7 and 8.) 
While the above changes are taking place the cells of the blastoderm crowd 
away from the sides, so that now it forms a band completely surrounding the 
egg. A dorsal view of this stage is seen in Plate II, figure 3. 
The fold noticed above makes the first segment of the embryo, the pro- 
cephalic lobes. It is pushed around to the ventral side of the embryo (PL II, 
figs. 4 and 5) and at the same time the ventral part of the fold becomes con- 
stricted laterally. Plate II, figures 1 and 2, are diagrams showing the relations 
of the parts of the fold, at this time, as viewed from the dorsal and ventral 
aspects respectively. The sides are next folded in in the line of the groove so 
that in ventral and dorsal views the procephalic lobe is plainly visible (PL II, 
figs. 6 and 7). A little later the infolding of the primitive band to form the 
stomodoeum begins, and at the same time a longitudinal groove, the gastrula 
invagination, extends along its ventral side. Plate II, figure 6-g, represents 
the first beginning of the gastrula infolding. 
F. FORMATION OF THE SEGMENTS. 
Following the gastrula invagination, and the formation of the procephalic 
lobes, the primitive band grows rapidly backward. The yolk is pus.hed up to 
the dorsal side, and the embryo lies as a band extending about the egg but not 
meeting on the dorsal side. As the primitive band extends backward from 
the procephalic lobes it becomes constricted by transverse furrows which 
divide it into segments. The mandibular segment is the first to appear, then 
the first and second maxillary segments. Following these, the segments ap- 
pear in a general way in succession from before backward. Frequently, how- 
ever, two or three segments seem to be formed almost simultaneously. 
G. THE PROCEPHALIC LOBES. 
In the first place the procephalic lobes are represented by a somewhat globu- 
lar fold at the anterior end of the primitive band (PL II, figs. 6 and 7). There 
soon appears on the ventral median surface on the fold a depression (PL II, 
fig. 8-a). As this deepens the anterior wall of the lobes is thickened and the 
lateral portions are pushed backward, forming a slight fold so that the pro- 
cephalic lobes proper become smaller in size. The mandibular segment crowds 
forward on each side apparently absorbing this fold. 
H. THE APPENDAGES. 
(a) The antennae. 
The antennae appear as buds from the base of the procephalic lobes just in 
front of the mandibular segment. They are first noticeable as small projec- 
tions near the dorsal part of the head (PL III, fig. 2-a). This takes place 
about the 30th hour of incubation. The antennal bud grows downward along 
