136 Bulletin of the Brooklyn Entomological Society Vol. XV 



of which I wrote him. Tillyard's reply was as given above, with 

 the further note that he started out to prove the oxygen theory 

 of fining and proved the opposite. 



7. Air of Transformation. 



(a) Filling of Pupal Trachece. — The process is slow. The 

 pupae of holometabola acquire practically a complete new system 

 of tracheae. This system, curious to say, fills with air from the 

 blood, and not from without. This can be readily demonstrated 

 by placing larvae about to pupate in deoxygenated water. 



(&) The Process of Transformation. — The process of final 

 ecdysis is primarily a process of inflation with air (Portier), so 

 that the enclosing chitinous envelope splits at a definite point. 

 Here we have what might be called internal inflation, and ex- 

 ternal inflation. 



Internal inflation occurs among hemimetabolic insects which 

 secrete air into the digestive tract (Portier) which swells like a 

 tube within a tire and breaks the outer shell of chitin. Portier 

 found the alimentary tract of transforming Odonata larvae enor- 

 mously expanded, its walls closely appressed to the body wall. 

 What the mechanism of secretion of air into the intestine con- 

 sists of must still be ascertained. 



External inflation occurs primarily among holometabola. Here 

 during pupation a layer of air can be seen to form between the 

 adult and the pupal skin proper. Take, for instance, a Chiro- 

 nomus pupa. The brown larva transforms intO' a red pupa — a 

 matter of a very few minutes — and through the skin the animal 

 can be seen. Soon one notices that within the pupal membrane 

 a second one has formed, a little later one notices a sheet of air 

 accumulating between the two. Contact with the outer air in 

 solution in the water is maintained through the cervical tracheal 

 tufts and the caudal tracheal plates. The amount of air increases 

 until the pupa becomes buoyant and slowly rises to the surface. 

 What is the air between the forming adult and the pupal skin? 

 Of course, it is easy to assume that it is probably oxygen, but an 

 assumption is not proof. One may equally well assume that it is 

 carbon dioxide, since during this period histolysis proceeds with 

 enormous rapidity and waste carbon dioxide is formed in quan- 



