Rl^AUMUR 269 



the transverse lines where the segments meet. Reaumur 

 took advantage of this arrangement whenever he had 

 occasion to extract a pupa from its shell. It still re- 

 mained to explain how the fly is enabled to open the shell 

 from within. Reaumur made the remarkable discovery 

 that the head of the fly is at this time capable of great 

 and rapid dilatation. All the fore part between the 

 compound eyes and the antennae can be distended so as 

 to double the size of the head. The fly, says Reaumur, 

 when it is ready to emerge, dilates its head with air, 

 and thus exerts a pressure sufficient to burst open the 

 shell. This statement contains the only mistake that I 

 have discovered in Reaumur's account of the trans- 

 formation of the blow-fly ; the head is not distended 

 with air, but with blood. Then the fly wriggles out, 

 relying at first upon its body-segments, but employing 

 its legs as soon as they become free. The delicate pupal 

 skin, which was closely fitted to every part of the 

 surface of the fly, is left behind in the empty shell, 

 and with it the linings of the air- tubes, which were 

 drawn out through the spiracles. The fresh-emerged 

 fly is soft and pale- coloured, and its wings are crumpled. 

 It looks too big for the shell in which it was imprisoned, 

 and is really so, for it enlarges after its escape in a 

 surprising way. Reaumur discovered that the enlarge- 

 ment is simply due to inflation by air, and by the prick 

 of a pin he was able to reduce the fly to its former size. 

 In the course of a few hours the skin darkens and turns 

 hard, the wings expand, and the insect becomes capable 



of flight. 



Aphids ^ 



Reaumur was able to make important contributions 

 to that investigation of the aphids, wliich Leeuwenhoek 



» Vol. Ill, M^m. ix. 



