268 



EMBRYOLOGY OF INSECTS AND MYRIAPODS 



the serosa. These membranes thereupon fuse as with the Odonata, 

 following which the embryo reverses its position until the head comes to lie 

 at the cephalic end of the egg, the embryonic envelopes accumulating 

 in the cephalic region, later to form the second dorsal organ. In this 

 revolution the grumulus is carried cephalad on the dorsal side of the 

 embryo and finally merges with and shares the fate of the embryonic 

 envelopes. Soon after the dorsal closure the insect emerges from the 

 chorion. 



po 



Fig. 196.^ — Toxoptera. Sagittal section, (abd) Abdomen 

 Labrum. (ov) Rudimentary ovary, (po) Polar organ, (ser) 

 daeum. (y) Yolk, (y 2) Degenerating ovarian yolk (mycetom). 



(am) Amnion. (Ir) 

 (stom) Stomo- 

 iyc) Yolk cell. 



HOMOPTERA 



Siphanta acuta 



The eggs of this species, as described by Muir and Kershaw (1912), are 

 long, cylindrical, flattened on the ventroanterior surface where the micro- 

 pylar area is situated, pointed at the anterior, and rounded at the poste- 

 rior end. The eggs are laid in batches of about 60, with the ventral side 

 uppermost, one overlapping the other. Twenty-four hours after the egg 

 is laid, the blastoderm is distinct, and a thickening along the dorsoposte- 

 rior area indicates the germ band. At about the thirtieth hour the poste- 

 rior end of the germ band begins to invaginate (Fig. 197) and is entirely 

 invaginated about the fortieth hour (Fig. 198), whereupon the amniotic 



