The Embryology of Chrysopa, and its Bearings on the Classification of the Neuroptera
Authors: Packard A. S. 
Published: April 2021

In a paper presented at the Burlington meeting of the Association in 1867,1 gave a brief sketch of the embryology of Diplax, especially in the later stages. Those observations, with the far more carefully elaborated studies of Brandt2 on Calopteryx, another member of the family Libellulidæ, have made us acquainted with the embryology of the type of one important division of Neuroptera, and now I have to offer a partial history of Chrysopa, the representative of another important division of the group. I did not observe the formation of the blastoderm, but the blastodermic skin (“amnion “) of Chrysopa, is of the same structure as in Calopteryx. At the posterior end of the egg the round nucleated cells are crowded together in the same way as in Calopteryx. The primitive band is of the same general form, and floats in the yolk as in Calopteryx, but more as in Aspidiotus, though it rests more on the outside of the yolk than in those genera, and the end of the abdomen rests on the outside of the yolk, rather than rolled in within the yolk; but that the germ is an endoblast (so far as that condition has any special significance) is shown by the fact that the dorsal side of the primitive band points inwards towards the centre of the yolk, as in the Libellulidæ, the Hemiptera, and a Coleopterous insect (Telephorus), in contradistinction to the Phryganeidæ and the Poduræ (Isotoma), in Which the germ or primitive band floats entirely on the outside of the yolk. After the procephalic lobes and rudiments of the appendages of the head and thorax have begun to develop, a second moult (visceral layer) of the blastoderm is made, which envelops the head and under side of the body much as in the Libellulidæ and Hemiptera. At this time the embryo is much like that of the last-named insects. The germ does not revolve in the egg, as in the Libellulidæ, hut the head remains throughout embryonic life next the micropyle. At the next stage observed, the appendages of the limbs had appeared, the embryo being situated on the outside of the yolk, the end of the abdomen curved around on the opposite side of the yolk. At this time the inner or “visceral layer,” forming a second moult of the blastoderm, envelops the germ, much as in the Libellulidæ, and Hemiptera, and Coleoptera (Telephorus). It is evident that this faltenblatt of Weissmann (or visceral layer of Brandt) is shed at a later stage than the “amnion “proper. This stage corresponds with that of Calopteryx figured by Brandt (pl. i, fig. 11). At this time the germ of Diplax and Calopteryx (Libellulidæ) floats within the yolk, but this difference I would regard as having no special importance, as in the Hemiptera the germ at the same stage of development rests on the outside of the yolk in Corixa, while in the Pediculina, according to Melnikow’s researches, the germ floats within the yolk, and we shall see farther on that in the Curculionidæ (Attelabus) the germ rests on the outside of the yolk (ectoblast), while that of Telephorus is a decided endoblast, i.e. floats in the interior of the yolk. After this period, the embryo of Chrysopa exactly corresponds to that of all the Libellulidæ whose development is known (Agrion, Calopteryx, Perithemis, and Diplax).