260 MR. F, BALFOUR-BROWNE ON THE [ Mar. 2, 
forward, and the head with the antenne and mouth-parts is drawn 
backward and upward out of the old skin and all these parts at once 
assume their normal position—the antenne pointing forwards, the 
labium doubling on itself and taking up its position below the 
mouth, the maxillz likewise bending forwards and coming to le 
on either side of the mouth immediately below the jaws. Further 
writhing of the abdominal segments forces the body still further 
out of the skin, and the legs are withdrawn from their sheaths. 
Once the legs are free, a final struggle clears the nymph of the 
pronymph skin. This latter is exceedingly thin and transparent, 
and almost invisible even under the microscope except for the fact 
that on each side of it is an irregular band of backwardly-turned 
projecting points. These lie scattered on either side of the thoracic 
and abdominal segments, but there is none on the head. These 
points are no doubt of use in assisting the pronymph to escape 
from the egg. 
Owing to scarcity of material after the discovery of the above 
details of the pronymph stage, I was able to observe the emerg- 
ence from the egg only in two or three cases, and I had not 
therefore opportunity of making many observations on the 
pulsating organ already referred to. Several points were, how- 
ever, noted. The organ is not far from the position of the 
mouth ; it contracts from in front backwards, apparently driving 
blood, since the corpuscles were visible, posteriorly, and the 
pulsation and direction of the flow were quite distinct. The 
drive was towards the dorsal surface near the posterior margin of 
the head, and a biood-vessel in that region (the aorta?) could be 
seen showing slight bulging each time the liquid was forced to it. 
Blood could also be seen passing from the anterior part of the 
head back to the pulsating organ; but at times this flow ceased 
and the corpuscles appeared to oscillate backwards and forwards 
at each beat of the organ, just as they may often be seen to do in 
the ordinary blood-spaces of the body. 
I could find no trace of a pulsating organ in the pronymph 
after it had escaped from the egg; but this might have been 
due to the fact that the creature was in constant movement 
for the two or three minutes of its existence. There is 
apparently no such organ in the nymph. I it only appears, 
as L believe, after the formation of the vesicle and disappears 
or ceases to pulsate as soon as the pronymph escapes from 
the egg, the obvious inference is that it has something to do with 
the emergence of the pronymph, and is, in fact, an embryonic 
organ. It is interesting in this connection that Wheeler (1893) 
has described an embryonic ‘ subeesophageal organ” as occurring 
in insects, of which he says the cells somewhat resemble those of 
the fat-body. He places it in the tritocerebral segment of the 
head, and says that it disintegrates in the larva. 
The function of the pulsating organ in the head of the Agrionid 
embryo seems to be to absorb the fluid in the vesicle, so as to 
allow the head to pass into it; but how it can do so is at present. 
