414 EMERGENCE OF DRAGONFLY-LARVAE, 



Only ill the case of the Pseitdosfiymatinrp does this inability seem 

 to have been removed (not unlikely, it appears, by bringing the 

 stigmata themselves int(j play for breathing air directly); and 

 the result has been, in this case, the evolution of a race of giants. 



Summary. 

 '\. Coiicl n.^ions fu hf drairn from Sections J -^ conceruirui An'iKop- 



terid larvce. 

 A. Tlic (rits in /ht' Tirichral System, and tit p Method of Ri'spiratioii 



(Sections 1 and 2). 

 1. Before hatcliing, the tracheal system of the embryo contains 

 no gas, but only a clear pale yellowish liquid, which is the liquid 

 portion of the insect's blood, resembling lymph. 



i. During the short pronymphal stage, this liquid is replaced 

 by gas throughout the legioii coterminous witli the midgut; I.e., 

 the gas enters practically simultaneously into the dorsal and 

 venti'al trunks and theii- five pairs of connecting tracheje in that 

 region. What happens in the visceral trunks could not be 

 observed. 



3. By a rapid extension, the gas passes forwards into the head, 

 and backwards into the posterior abdominal segments, until it 

 fills the whole tracheal system, including all the capillaries of 

 the rectal gills. 



4. The gas in the tracheie is almost certainly carbonic acid gas. 



5. Regular respiration via the recti;m sets up a process of 

 difi'usion between the capillaries of the rectal gills and the cir- 

 cum-ambient water, so that C'O^ passes out into the water, and a 

 mixture of O and N, closely resembling air, passes into the 

 capillaries, until, finally, the partial pressures of all these gases 

 become the same in the tracheal system as in the water {i.e., N, 

 610 mm.; O, 150 mm.; COo, less than 1 mm.). The experiments 

 suggest that a considerable time must elapse before this final 

 equilibrium is fully established. 



B. The Nature and Action of the Cephalic Heart (Section 3). 

 While this f)rgan could not be examined actually in situ and 

 in action, the following suggestions ai-e made concerning it, and 



