404 EMERGENCE OF DRAGONFLY-LARV^, 



is only in action fpr about half-a-minute, it is most difficult to 

 determine its exact nature and position. We know that it is 

 situated above and somewhat posterior to the mouth, and below 

 the dorsal aorta; that at first it is very small, that it increases 

 rapidly in size and in the force of its pulsations; and then, after 

 performing about twenty-five I'egular double-beats in half-a- 

 minute, subsides veiy quickly. In appearance, it is two-cham- 

 bered, but whether there are actually two pulsating chambers, 

 or a single one constricted at some point by the tentorial 

 structures of the head, I had not been able to determine. With 

 Balfour Browne,*! agree that this organ pumps a pale yellowish 

 liquid, which can be none other than the liquid part of the blood. 

 I did not observe any corpuscles passing through the organ. 

 Balfour-Browne states that the blood is pumped upwards and 

 backwards. This appears to me also to be correct as regards the 

 first few pulsations of the organ; after that, I confess that 1 

 could not follow a definite course of the blood, and I must hold 

 to the opinion that most of the blood pumped into the anterior 

 chamber (or auricle, as I previously termed it) was again pumped 

 out into the posterior chamber (or ventricle), and served to cause 

 the immense distension of that chamber which takes place just 

 before the larva bursts its pronymphal sheath. What the exact 

 nature of the organ is, and whence and whither the blood was 

 actually pumped, I had not been able to determine. 



In entering upon the experiments already detailed in Section 

 1 of this paper, I had strong hopes that the general retardation 

 of the process of hatching might be accompanied by a correspond- 

 ing I'etardatioii in the action of the cephalic heart, and that thus 

 T might be able to examine this oi-gan more minutely. It will 

 be seen already, however, that these hopes were frustrated, since 

 the cejahalic heart barely came into action before it subsided 

 again, at the birth of the pronymph, and failed altogether to 

 come into action again during the whole of the pronymphal 

 stage, lasting over three hours. Indeed, it is very probable that 



""The Life-Historj' of the Agrionicl Dragonfly." Proc. Zool. Soe. 

 Loudon, UHKI, pp.2u3-"285. 



