564 EMBRYOLOGY OF CHRYSOPA. 
constancy of specific characters. These, he showed, remained 
unaltered throughout great extents of time and space, and other 
slight structural characters endured through many geologic ages. 
Hence the value of cases where the association of characters is 
evidently in a transitional condition. 
Tur EMBRYOLOGY or CHRYSOPA, AND ITS BEARINGS ON THE CLAss* 
LFICATION OF THE NeuROpTERA.—By A. S. PACKARD, JR., M.D. 
Ix a paper presented at the Burlington meeting of the Associ- 
ation in 1867, I gave a brief sketch of the embryology of Diplax, 
especially in the later stages. Those observations, with the far 
more carefully elaborated studies of Brandt * on Caloptéryx, an- 
other member of the family Libellulidz, have made us acquainted 
with the embryology of the type of one important division of Neu- 
roptera, 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 blasto- 
dermic skin (‘‘amnion”) of Chrysopa, is of the same structure as 
in Calopteryx. At the posterior end of the egg the round nucle- 
ated 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 ventral side of the primitive band points inwards 
towards the centre of the yolk, as in the Libellulide, the Hem- 
iptera, and some Coleoptera (Telephorus and Donacia) in contra- 
distinction to the Phryganeide 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 appen- 
dages 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 Libellulide 
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 
* Beiträge zur Entwicklungsgeschichte der Libelluliden und Hemipteren. St. Peters- 
burg. 1869. 
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