400 EMERGENCE OF DRAGONFLY-LARVii;, 



Result : — The rectal capillaries collapsed in from 2-3 hours, the 

 main tracheal system (whole length of dorsal trunks) in from 5-6 

 hours. 



Experiment 1. — Two larvse, aged from one to two days old 

 (strongly pigmented), were placed alive in 10% solution of KOH. 

 The solution was regularly sucked into the rectum and expelled 

 again, causing considei'able irritation to the larvae, both of which 

 died within an hour. A close examination showed that the 

 rectum became swollen and somewhat opaque. The rectal capil- 

 laries remained quite unaft'ected, except where the gill-tissues 

 became very badly damaged. The main tracheal system was not 

 aifected in any way. 



Conc/vsion. — No appreciable CO.^ present in tlie tracheal 

 system of larvae 1-2 days old. 



Experitnent 2. — Two larvse, which emerged from Series C on 

 Api'il 4th, were taken before they were two houi's old, and placed 

 alive in 10% solution of KOH. Both died within half-an-hour, 

 after having repeatedly sucked the solution into the rectum and 

 expelled it again. In three-quarters of an hour, the doi'sal 

 trunks began to collapse from the region of the rectum forwards, 

 but the i-ectal capillaries remained unaltered. At one hour, the 

 dor.sal truidvs were very badh' collapsed. At two hours, all the 

 trachea^ in the abdomen had collapsed, except the rectal capil- 

 laries, which remained only partially collapsed. At three hours, 

 tlie whole tracheal system had collapsed, including the parts in 

 the head and thorax, but there still remained a number of the 

 rectal capillaries only partially collapsed. At four hours, all the 

 capillaries had collapsed {of. Control Experiment). 



Conehision. — The gas in the tracheal system of larva? 1-2 hours 

 old is CO 2, except in the rectal capillaries, which are, at any 

 rate, partially filled with some gas not extracted by KOH. 



Experiment 3. — Two larva? were taken from Series B and C 

 respectively, the latter between two and three days old (sti-ongly 

 pigmented), the former between six and twelve hours old (just 

 beginning to become pigmented), were placed alive in 4 % solu- 

 tion of Azol. The larvae lived for two or three hours, and ap- 



