OXYGEN AND RESPIRATION 103 



parasites of the termite gut (Cleveland, 1925). Kitching (1939a, b) 

 has found that cilia of free-living ciliated protozoa ceased to beat 

 in the absence of oxygen, and that cilia of the peritrichs Cothurnia, 

 Vorticella and Zoothamnium stopped within 5 to 15 min, while 

 those of Paramecium continued to beat for an hour or more. 



The close link between respiratory activity and the movements 

 of cilia and flagella established by these studies is to be expected 

 in view of the constant supply of energy required for these 

 movements. It is also not surprising that cilia and flagella may be 

 used in anaerobic conditions by organisms which have been able to 

 release energy for other vital activities in the absence of oxygen. 



The route of supply of energy from the reserve substances to 

 the ciliary mechanism is now fairly well known. Spermatozoa of 

 both vertebrates, e.g. bull (Mann, 1954), and invertebrates, e.g. 

 sea urchin (Rothschild and Cleland, 1952; Mohri, 1957a), seem 

 to carry phospholipids as an energy store, and, in the absence of 

 other available substrates, these are broken down to provide 

 energy for movement. Carbohydrate is present in mammalian 

 semen, however, and this is broken down (although usually only 

 anaerobically to lactic acid) to provide energy for sperm motility 

 in preference to the phospholipid stored in the sperm. Glycogen 

 seems to form the energy store in the gills of the oyster, and 

 Usuki and Koizumi (1954) have found that seasonal changes in 

 ciliary activity and changes in the glycogen content of the gills 

 show similar trends. The most important substrates in ciliated 

 tissues are probably carbohydrate, in spite of the fact that Gray 

 (1924) found a respiratory quotient of 0-84 in My tilus gill. Both 

 carbohydrate and phospholipid can be broken down by processes 

 involving the tricarboxylic acid cycle after preliminary stages 

 which are different for the tw^o substrates. The main stages in 

 these degradations are shown in Figs. 26-28. 



Observations w^hich confirm that the breakdown of these 

 substrates by this route provides the energy required for the 

 activity of cilia and flagella may be summarized as follows: 



(i) Monoiodoacetic acid inhibits the activity of cilia of the 

 oyster gill (Usuki, 1956a), lateral cilia of My tilus gill (Aiello, 1960) 

 and sperm (Mann, 1954). It blocks stage 7 (and also stage 23), 

 and results in the accumulation of glyceraldehyde-3 -phosphate 

 in oyster gill tissue (Usuki and Okamura, 1956). 



