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SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 1 39 



surface of the water, any of them can stay below without apparent 

 discomfort, and some do so indefinitely. It was formerly supposed 

 that the four thin-walled tracheated lobes borne on the end of the 

 tenth abdominal segment were gills serving for underwater respira- 

 tion. Wigglesworth (1933), however, has produced evidence that 



Fig. 11. — Respiratory tubes of larvae and pupae that get their air from the 

 roots of aquatic plants. 



_ A, Mansonia indxibitans, terminal segments of larva. B, Same, apical part of 

 siphon, ventral. C, Mansonia sp., thoracic respiratory horns of pupa, dorsal. D, 

 Same, right horn, mesal. E, Mansonia richiardii, pupal respiratory horns, dorsal 

 (from Wesenberg-Lund, 1920-21). F, Ficalbia hybrida, terminal part of pupal 

 respiratory horn (from Bonne-Wepster, 1932). 

 An, anus; Tra, trachea. 



these lobes are water-absorbing organs rather than gills. By immers- 

 ing larvae in a water culture of the flagellate protozoon Polytoma, 

 which is highly sensitive to the amount of oxygen in the water, he 

 found that the flagellates first assemble at the posterior end of the 

 larva and then spread all over the body surface. Soon, however, they 

 move away in a mass, indicating that oxygen is being consumed by 



