394 EMERGENCE OP DRAGONFLY-LARV^, 



forwards. The (esophageal valve became deeply sunk into the 

 midgut, where it was worked strongly up and down. The mid- 

 gut was gradually forced further and further forward, until it 

 came to occupy a considerable part of the thorax, as well as the 

 first three or four abdominal segments. At the end of an hour, 

 the pulse had dropped to 4<S; after three hours, it had fallen to 

 44. Half-an-hour later, it was down to 40. It then appeared 

 that the pronymph was completely exhausted. I therefore re- 

 moved it to a watch-glass, and fixed it immediately in hot Avater 

 at 95^C. 



It will be seen that this pronymph existed for about three and 

 a half hours, and never succeeded in bursting open its sheath. 

 During all this time, my attention was principally concentrated 

 upon the tracheal system. As both egg-shell and pronymph 

 lay upon their sides, and as the struggles of the latter to free 

 itself were not sutiiciently violent to displace it from this favour- 

 able position, I had a unique opportunity of watching for the 

 appearance of gas. When the pronymph first emerged from the 

 egg-shell, the whole tracheal system was clearly filled with a pale 

 yellowish Huid (which could scarcely be anything else than the 

 clear litjuid part of the blood) without any corpuscles. A simi- 

 larly coloured licpiid could be seen passing along the dorsal 

 vessel, accompanied by a small number of oat-shaped corpuscles. 

 The whole head-cavity, and all the thorax and abdomen, except 

 the midgut, also apjaeared to be full of the same coloured liquid. 

 The midgut showed up as a darker cylindrical barrel or plug, 

 evidently enclosing the remains of the yolk. The dorsal tracheal 

 trunks could be easily made out, and their prolongations into the 

 head could be followed as far as the eyes. The rectum could be 

 distinguished, but no details of the tracheation of the gills could 

 be made out. The \'entral trunks could be picked up only with 

 flifiiculty, as they were so much smaller than the dorsals. At no 

 time was I able to see the visceral trunks, owing to the dark 

 mass of the midgut being placed so close to them. 



For three hours, I watched the tracheal system of this pro- 

 nymph iritlwHf detecti'ity (uiij sign of y<(s In it. A few minutes 



