IOWA ACADEMY OF SCIENCE 
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a circle of cilia about their external opening. These are in connection with the 
tracheal system, a tube from which extends along their entire length, opening 
at the distal extremity. They serve as larval respiratory organs. They may 
be seen in the embryo in figure 7, Plate III, r., and in the newly hatched larva. 
DESCRIPTION OF PLATE I. 
Fig. 1. The egg 2 or 3 hrs. after laying. (a) Large, cells which later develop into 
the reproductive organs. - - - - - • - • - 
Fig. 2. The eggs at about 2 or 4 hrs. showing the layer of blastodermal cells, (a) 
Large reproductive cells. 
Fig. 3. The egg at about an hour later than in fig. 2, showing the thickened layer of 
blastodermal cells, and the large reproductive cells still visible at a. v 
Fig. 4. The egg at about the sixth hr. of incubation. v-K \ 
(a) reproductive cells. [• 
(b) cells arranged in a columnar layer forming the blastoderm. 
Fig. 5, The reproductive cells have retreated to the. interior and are no longer visible, 
(p) The beginning of the primative band. 
Figs. 6 and 7. A little later than 5, showing the first infolding of the blastoderm, 
(v) Vitelline membrane. 
Fig. 8. Egg at about hr. of incubation. (v) Vitelline membrane. (p) Begin- 
ning of stomodoeum. 
DECRIPTION OF PLATE II. 
Figs. 1 and 2. Diagram showing the form of the first fold at the anterior end. In fig. 
1 as viewed from the dorsal and fig. 2 ^s viewed from the ventral sides. 
Fig. 3. Dorsal view at the same stage showing the yolk mass crowded to the sides, the 
blastoderm forming a complete dorso-ventral band. 
Figs. 4 and 5. Showing the fold pushed to the ventral side and baclgvards. 
Fig. 6. Ventral view of embryo. (p) procephalic lobe. (g) beginning of gastula 
invagination, (s) beginning of proctodoeum. 
Fig. 7. Dorsal view of stage shown in fig. 6. (p) procephalic lobe, (s) proctodoeum. 
Fig. 8. Egg at about eighth hr. of incubatiori. (v) Vitelline membrane. ,(p)‘-Begin- 
(m) Mandibular segment, (g) Gastrula. 
Figs. 9 and 10. Two views about 4 and 7 hrs, later than fig. 8, showing the divided 
mandibular segment (m) pushing upward on each side of the procephalic 
lobes and carrying with it the antennal point (a). - - " 
Fig. 11. Dorsal view of embryo at same stage as fig. 10. 
Fig. 12. Ventral view of embryo at same stage as fig. 10. ( m )■'' Divided mandibular 
segment. 
DESCRIPTION OP PLATE III. ; - 
Pigs. 1 and 2. Two views of the anterior parft of the embryo at about 28 hrs-32 hrs. 
(a) antennae (md) mandibular segment. (1 mx). First maxillary segment. 
(2 mx) second maxillat-y segment. v,. . V 
Fig. 3. Side view of the entire embryo a little later' than in fig. 2, showing thoracic 
and abdominal segments. Lettering as in fig. 2. 
Pigs. 4, 5, and 6. Dorsal ajid' ventral views of the anterior Portion of the embryo, and 
entire side view at about 40 to 45 hrs. Lettering as in fig. 2. 
Fig. 7. Ventral view of embryo at about 55 hrs. to 60 hrs., showing mandibles begin- 
ning to form (md) and respiratory appendages at r. 
Pigs. 8 and 9. Side and ventral views about 5 hrs. later than fig. 7. 
Figs. 10 and 12, Side and ventral views of the anterior and of the embryo just before 
hatching. Lettering as in figs, above. 
Pig. 12. Side view of the entire embryo just before hatching. 
Fig. 13. Optical section of embryo just before hatching, showing proctodoeum, stomo- 
doeum, nerve-cord, and the still prominent sexual cells. 
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