DEVELOPMKNT OF THK COASTAL RELT OF SOUTH AFRICA. 225 



We thus get a vision of our 85,000 square miles of coastal 

 land as the great industrial centre of the future, carrying a 

 population to the s(juare mile as large as in England, namely, 600. 

 This means a total population of over 50,000,000. As America 

 jumped into a great nation during the nineteenth century, so we 

 may look forward to South Africa jumping into a great nation 

 during the twentieth century, and the first great step is to dam 

 our rivers. 



PHYSIOLOGY OF RESPIRATION IN SO^JE AQUATIC 



INSECTS. 



By S. G. Rich. M.A., B.Sc. 



Read July 9, 1919. 



The present paper arises out of the apparent attempt of 

 some recent workers to compare the respiration of insects with 

 that of vertebrates. 



In vertebrates there is always a double process of respira- 

 tion. In gills or lungs, or through the skin, the oxygen of the 

 air passes into the blood, where it unites with the haemoglobin in 

 the corpuscles to form oxyhremoglobin. The oxygen, thus fixed, 

 is carried to the tissues by the circulation of the blood. Arrived 

 in contact with the cells of various tissues, the oxyhsemoglobin 

 yields up its oxygen for intra-cellular respiration. We thus have 

 two stages in the oxygenation of the cells. In exactly a similar 

 manner, the cells yield up their excreted carbon dioxide to the 

 haemoglobin, which carries it to the lungs, gills, or skin, through 

 which it diffuses into the air. In saying " air " I here include 

 the air dissolved in water in the cases of gill-breathers. 



In all save a few special cases the blood of insects has thus 

 far failed to show the presence of either of the oxygen-carrying 

 substances known to physiologists : haemoglobin and hsemo- 

 cvanin. The cue definitely proven occurrence of haemoglobin in 

 an insect is in the familiar " bloodworm " of our streams, the 

 larva of the dipterous insect Chironormis. It is possible that the 

 larvcC of some few Trichoptcra contain haemocyanin in their deep- 

 green blood. 



In connection with the well-known groups of insects possess- 

 ing tracheal gills, and respiring air dissolved in the water which 

 they inhabit, recent workers have attempted to explain the phy- 

 siology of respiration. Bodine (1918), working on dragon flies 

 of the family Agrionidcc, in the larval stage, showed that the sup- 

 posed external tracheal gills of this family were not functional. 

 Removal oT these alleged gills interfered in no way with the 

 life and metamorphosis o^f the larvae. Finding that the rectal 

 tracheation was wholly insufficient to allow of the passage of 



