Fig. 2
a Schematic experimental set-up to study the diffusion of CO2 from inside to outside the cocoon: The dead pupa was removed from the cocoon by making a narrow cut at the top of the cocoon and this cut was sealed by wrapping with a narrow band of para-film keeping the surface intact. A narrow glass tube was inserted on the top of the cocoon to supply CO2 gas. The cocoon was allowed to hang in an air-tight beaker container containing Ca(OH)2 solution. CO2 was generated as shown in the figure using CaCO3 and dilute HCl solution. As soon as CO2 gas was allowed to pass inside the cocoon through the glass tube, the CO2 started diffusing out of the cocoon. We recorded the time as soon as we observed the appearance of milky white smear on the Ca(OH)2 solution. b Schematic experimental set-up to study the diffusion of CO2 from outside to inside the cocoon: the dead pupa was removed from the cocoon and the cut was sealed by para-film. A narrow glass tube was inserted into the cocoon and the other end of the tube was immersed in Ca(OH)2 solution in a beaker which was maintained under the blanket of argon flow to prevent contamination from aerial carbon dioxide. The cocoon was hung in an air tight beaker having an inlet for the passage of CO2 with a narrow hole at a distance for free gas passage. Sometimes we blocked this narrow passage to generate CO2 pressure on the outer surface of the cocoon. The generated CO2 gas was allowed to pass for more than 10 min. We performed this experiment on 11 different cocoons (n = 11) and in each case the Ca(OH)2 solution remained unaffected. c Schematic experimental set-up to study the diffusion of O2 from inside to outside the cocoon: the experimental set-up was similar to the CO2 detection setup. Except O2 detection was done by using sodium pyrogallate as an absorbent. On absorbing O2, the color of the sodium pyrogallate solution changes to dark brown. This experiment needed an extremely inert environment. Inert environment was created by purging the set-up with excess argon gas. When under argon purging the pyrogallol solution remained pale yellow, the valve of the oxygen cylinder was opened very gently and within minutes the indicator solution turned deep-brown showing the diffusion of O2 from inside to outside of the cocoon membrane. The experiment was repeated with 10 different cocoons showing the same result. d Schematic experimental set-up to study the diffusion of O2 from outside to inside the cocoon: the preparation of empty cocoon was done as described earlier. The alkaline pyrogallol solution was placed under constant argon purging to avoid interaction with air. The set up was first purged with argon for 30 min and then a flow of oxygen gas was introduced. Within minutes the pale yellow pyrogallol solution turned deep brown. The experiment was repeated with 10 different cocoons showing the same result