1807.] 119 [Trouvelot. 



When the expansion of the wings takes place, it sometimes hajipens 

 that the wings swell up at one or several points. This swelling is 

 caused by the fluid which issues from the abdomen of the in- 

 sect for the purpose of developing the wings. This fluid accumulates 

 between the two thin membranes covering the costie, where obstruc- 

 tion in the vessel oifers some resistance to its circulation, and so to the 

 expansion of the wing ; or a too dry atmosphere, by causing a rapid 

 evaporation, Impairs the necessary elasticity, and prevents their due 

 development. Generally the pressure of the fluid from the abdomen 

 is sufficient to overcome the difficulty, but sometnnes the obstruction is 

 so great, and to ovo'come it so much fluid is emitted, and with so 

 great pressure, that the thin membrane of the wings can no longer re- 

 sist the tension, and It bursts open where the fluids have accumulated, 

 and they flow out. As these fluids are absolutely necessary for the 

 expansion of the wings, their loss is the cause of the imperfect devel- 

 opment, and when once they are lost, the expansion of the wing 

 ceases entirely ; nevertheless the other wings will continue to develop, 

 the loss of the fluid of one wing having no influence whatever upon 

 the growth of the othei's ; probably each wing has a separated reser- 

 voir containing the fluids necessary for its development. This seems 

 to be visible in the abdomen, as sometimes four distinct swellings are 

 seen. 



I have artificially produced this monstrosity in the wings. Observ- 

 ing a Lepidopteron just emerged from the pupa, I saw a large swelling 

 on the discoidal cell on one of tlie wings, and pierced it with a needle ; 

 the fluid flowed from the puncture, and immediately the wing so 

 wounded ceased to grow, while the three others continued their de- 

 velopment to its flill extent. The insect thus obtained was compara- 

 tively perfect, having only one wing smaller than the others, but well 

 proportioned. 



I have sometimes advanced the development of the wings of Bom- 

 hyx Polyphemus. I selected for this purpose pupse very far advanced 

 in their transformation, as is shown by the looseness of the pupal 

 skin, and by the color of the wings of the moth, which can be seen 

 through it. I took carefully the pupal skin from around the moth 

 and suspended the insect in the position that Lepidoptera take when 

 emerging from the chrysalis. It Is very rarely that the wings of 

 such an insect are developed, though I have obtained some perfect 

 specimens in this way ; and In one Instance the development of the 

 wings took place only three days after the pupal skin had been re- 

 moved. Success is more certain If the insect is put under a glass jar 

 Avith a moistened sponge, and something for the insect to hang from ; 

 the dampness of the air in the jar will prevent the soft wings from 

 drying too fast, and when the time arrives for the Insect to accom- 



