Dec, 1920 Bulletin of the Brooklyn Entomological Society 135 



Franckenberg calls it oxygen. Franckenberg postulates some 

 gland in the embryo which is able to fix oxygen in considerable 

 quantities, and that this oxygen is so loosely bound that it disso- 

 ciates with nearly explosive force (in fact, the explosions dis- 

 rupt the air chambers and the larva itself when put under dimin- 

 ished pressure), pushing the serous fluid before it in its progress 

 through the tracheae toward the head. The gland Franckenberg 

 locates behind the posterior chambers in Corethra. In proof he 

 cut off the posterior of the larva and prevented a filling. If he 

 cut in front of the posterior chambers, these filled up. Another 

 proof is adduced: the air in solution in the water in which the 

 embryo lay was analyzed. The embryo was then removed to 

 deoxygenated water for a few minutes until its tracheae filled 

 with air. This tracheal air was then analyzed and found to be 

 the same in the chambers as in the water from which the embryo 

 had originally been taken. On this basis Franckenberg postulates 

 some gland able to fix oxygen in quantities and carry it over till 

 needed. 



In contrast to this Tillyard experimented with potassium hy- 

 droxide and baryta water, to ascertain the composition of the 

 air in the tracheae immediately after filHng. The chemical tests 

 satisfied him that it was carbon dioxide. Tillyard states that the 

 process is a purely mechanical one, that the CO2 represents the 

 waste accumulations of the histolytic processes of the embryo, 

 "which go out of solution with sufficient force to displace the 

 serous fluid that filled the tracheae primarily. The process is 

 analogous to the behavior of carbonated water. Release the 

 pressure, and the carbon dioxide goes out of solution at once, 

 effervescing freely. The same may be observed when water is 

 taken from the bottom of deep lakes and exposed to the air; the 

 carbon dioxide goes out of solution with much hissing and ef- 

 fervescence. 



Tillyard's theory is probably the better of the two. Since 

 Franckenberg's analyses were not made until some time after 

 filling of the tracheae, it is probable that the carbon dioxide had 

 already diffused through the cuticle and was replaced by oxygen 

 from the water or blood (see section 7). At the time Tillyard's 

 paper was published he did not know of Franckenberg's work, 



