STRUCTURE OF WINGS. 343 



of a thick structure and easily expanded. They differ 

 in this from full-formed wings, which cannot be stretch- 

 ed a hau-'s breadth without tearing them; whereas we 

 have taken the wing of a butterfly on its emerging 

 from the chrysalis, and extended it to four times its 

 original expansion. That the fluids of the body are 

 at this period impelled into the wings, is proved by 

 an experiment first tried, we believe, by Svvammer- 

 dam, on the wings of bees. ' The blood in the bee,' 

 he says, ' is a limpid fluid, as may be observed, if a 

 little part be at this time cut off* from the wings; for 

 then the fluid exudes from the cut part, appearing, by 

 reason of the extreme smallness of the blood-vessels, 

 under the form of little pellucid globules, which in- 

 sensibly and by degrees increase into considerable 

 little drops.' — 'The wings of the bee have likewise 

 many pulmonary tubes, which, when the nymph is 

 casting its last skin, have also, together with all the 

 other parts, once more to throw off their exuviae. 

 After this, when these tubes are again distended by 

 the freshly impelled air, and the air-vessels, which 

 have hitherto been contracted, are inflated and dis- 

 tended with the same air, it follows that the whole 

 wing afterwards expands itself, and becomes thrice, 

 nay, four times larger than it was before. This ex- 

 pansion of the wings depends, therefore, both upon 

 the impulsion of the air and of the blood; for at the 

 same time when the air is impelled into the wings, a 

 considerable quantity of blood is likewise driven into 

 the vessels of the wings.' — 'The female bees do not, 

 as the common bees and the male, come forth with 

 their wings folded up, but expanded and displayed, 

 and in a state ready for flight. On this account, the 

 all-wise Author of Nature has provided for them a 

 more spacious mansion, in which they may expand 

 their wings conveniently and properly; so that after 

 they have burst from their cells they may be pre- 



