April, 



1905, 



KNOWLEDGE & SCIENTIFIC NEWS. 



79 



How is the unfolding done? It might be supposed, | shown by the fact that if the wing is injured at this 

 from the fact that such a large number of the heavier stage large drops of emerald green fluid are extruded, 

 insects climb up some support and let the wings hang An instance'of this came under my notice ; this particular 



..sect hanging erect, the 

 beginning to unfold. 



Fig- 3— The wings unrdding, the abdo 

 strongly bowed and much distended. 



Fi2.4.— The wings unfolding, the abdomen 

 strongly bowed and much distended. 



down as they expand, that the weight of the wings 

 alone would account for the unfolding; this, no doubt, 

 is a considerable help, but it is not sufficient to account 

 for the perfect flatness ultimately obtained, and, more- 

 over, it takes no account of those winged insects which 

 do not hang themselves up, the common gnat, for 

 instance. 



We may reject, I think, the notion that air is in- 

 jected, as that would probably cause a certain " puffi- 

 ness " in the wing, of which there is no sign. I hope 

 to show that the expansion of the wing is effected, in 

 one instance at least, by the injection of fluid, and thus 

 it is a spontaneous action, and entirely under the 

 control of the insect itself. 



Now, in the case of the dragon-fly illustrated, the 

 insect, on emerging, hangs head downwards for some 

 little time, for twenty minutes or more ; during that 

 time there is not the smallest tendency of the wings to 

 unlold, but directly the second stage of emergence is 

 reached and the insect hangs right way up, the wings 

 begin to unfold at once ; careful observation will show, 

 moreover, that the unfolding is not continuous nor 

 regular as if the creases were simply falling out, but 

 is by fits and starts, and that these irregular movements 

 correspond exactly with great muscular efforts, the 

 segments of the abdomen are contracted, and the im- 

 pression given is that of someone taking a deep breath 

 and exerting great force. Occasionally there are 

 spasmodic jerks and quiverings, as if to' shake loose 

 the folds of the wings. All this time the abdomen is 

 strongly bowed to the exact curve to be occupied by 

 the wing, no doubt to avoid injurv to the excessively 

 tender fabric of the wing. It is scarcely possible to 

 doubt that the wings are being forced out of their 

 folds by the muscular energy of the insect. 



And that it is fluid which is injected seems to be 



Fig. s.-The abdomen straight, wings nearly dry. 



insect was injured by a grass stem, and the wing did not 

 recover, it remained crumpled and was a complete 

 failure. 



