BY R. J. TILLYARD. 389 



common Water-lVEilfoil {Myriopkijlhivi sp.) containing more than 

 sixty eggs of Anax papuensis. These eggs were laid in a regular 

 spiral, down the stem, throughout a distance of about five inclies 

 in length, viz., that part of the stem from about an inch l)e]o\v 

 water-level downwards. In the present paper, I propose to give 

 an acc(junt of the important results obtained from some experi- 

 ments carried on \\ ith these eggs, together with some further 

 observations made upon the eggs of a Zygopterid dragonfly, ob- 

 tained from the same locality in November, 1915. These latter 

 were not determined with certainty, but there is little doubt 

 that they belonged to Austrolesf.es leda Selys, a very common 

 species around Sydney. 



1 desire to thank Dr. H. G. Chapman, Lecturer in Physiology 

 in the University of Sydney, for some valuable suggestions and 

 advice in connection with the experiments carried out on the 

 eggs of Anax. 



I propose to divide this paper into five sections, dealing with 

 the several problems which present tliemselves for solution. 

 These are : — 



1. The exact origin of the first gas in the tracheic of the 

 emerging larva. 



2. The composition of the gas in the tracheal system. 



3. The nature and action of the cephalic heart. 



4. The eliect of abnormal conditions upon embryonic dexelop- 

 ment. 



5. Kectal respiration in newly-hatched Zygopterid larviv. 

 Sections 1-1 represent the studies carried out on Anax papu- 



i^»cS'i*'(Anisoptera); Section 5 those on An ><f rol cstes I rd(i{'/Ay^ffo\)ievA) . 



Section 1. — Tlv Exm-t Orujln of ilw Jirsf (riix in fh<- TrarJiar of 



the BmeryiiKj Larrn. 



hi my former account of the emergence of the lar\a of Anax. 

 jiapiiensis from tlie egg, I pointed out how difficult it was to 

 make accurate observations, owing to the rapidity with wliich 

 the hatching takes place. The pronymphal stage lasts only a few 

 seconds, and the whole period of emergence occupies only half-a- 



