302 



INSiiUT TRANSFORMATIONS. 



issuing by jets, and a few smaller bubbles over the 

 body of the chrysalis, probably from not taking the 

 precaution afterwards suggested by Bonnet, of moist- 

 ening it before immersion.* 



Upon examining the structure of the spiracles, 

 M. Reaumur further discovered that their mouths are 

 furnished with ciliary valves, which are shut when 

 the pupa is plunged into water, but opened again 

 when it is taken out. This circumstance accounts for 

 the swelling of the body under the exhausted receiver 

 of the air-pump, for it may be supposed the animal 

 would closely shut the valves when it felt the air for- 

 cibly extracted from its body. It is remarkable, 

 however, that though the shutting of the valves pre- 

 vents the entrance of water, it has not the power of 

 excluding oil ; because, as Reaumur conjectures, it is 

 not in the ordinary course of its nature exposed to 

 such an accident, and therefore Providence made no 

 provision for it.f It may be recollected that the 

 larvse of the cheese-fly and of blow-flies are provided 

 with a sort of valve, with which they can cover such 

 of their spiracles as become immersed in any greasy 



Spiracles of pupcc. a, the valve open ; b, the same shut. 



In the aquatic pupa, of the ringed China-mark 

 moth (Hydroeampa stratiotata, Stephens) De Geer 



* Bonnet, CEuvres, vol. iii. p. 39, &c. f Mem. i, 407, &c. 

 I See page 265. 



