1909. | LIFE-HISTORY OF THE AGRIONID DRAGONFLY. 261 
amystery. In the embryo of the water-beetle (Hydrobius fuscipes 
L.) I find that there is a cephalic pulsating organ which becomes 
active a few hours before the escape of the embryo from the egg, 
and that during its activity the embryo enlarges so as to completely 
fill the egg. There is, however, no vesicle formed, and in that 
case I am almost certain the pulsating organ is not a special 
structure but merely a pharyngeal pump, which is found in the 
larva after its emergence and is similar to that in all suctorial 
insects. In the Agrionid nymph, however, there is no suctorial 
apparatus ; apart from which, the blood-corpuscles visible in the 
pulsating organ oppose the idea that it is part of the alimentary 
canal. 
Civeulatory pumps, accessory to the heart, have already been 
described in insects, but so far, I believe, they have only been 
observed in imagines and ase and not as embryonic organs. 
Behn (1835) first discovered them in the legs of various Hemipter a, 
and Selvatico (1887), Pawlowa (1895), and others have described 
them in the heads of certain Lepidoptera and Orthoptera. 
Selvatico describes an enlargement at the anterior end of the 
aorta—the ‘ frontal sac,” a description which might possibly suit 
the organ in the Agrionid embryo. 
The reversal of the blood-stream observed in the embryo is also 
not unique*, as Bataillon (18935) observed the same phenomenon 
in the pupa of the silkworm. 
With regard to the formation of the vesicle, it is possible that 
it is due to the displacement of the fluid which presumably 
surrounds the embryo within the shell, or possibly the fluid is 
extruded from the embryo to be later reabsorbed. 
Much, however, remains to be discovered with regard to these 
phenomena i in the egg. 
THe Nymex. Stage 1. 
The nymph which escapes from the pronymph skin is no longer 
than the pronymph, in fact the total length—not including the 
caudal lamellee—is just about that of the egg from which it came. 
It consists of a head, 3 thoracic and 10 abdominal segments, and 
is an excellent example of the campodeiform larva. The head 
bears two antenne, each of which consists of 3 segments, two 
basal ones, which are of characteristic form and except in size do 
not show any change during the life of the nymph, and a long 
bluntly pointed, slightly ineurved apical one. Not far from its 
apex, and on its outer side, this apical segment bears a very small 
spur. The length of this segment is equal to about 70 per cent. 
of the whole antenna. 
The mouth-parts consist of a pair of jaws of the usual 
* I have recently observed a reversal of the blood-stream in the heart of a well- 
grown nymph, and I imagine the blood was also passing into the last chamber of 
the heart by the last pair of ostea. It was escaping by the ostea in the 8th abdominal 
segment. 
