122 FACTORS AFFECTING CILIARY ACTIVITY 



branchial nerves do not enter the gill filaments, so that the lateral 

 cilia are unlikely to be under direct nerv^ous control. These 

 lateral ciUa cease their activity shortly after the gill filaments are 

 isolated from the body, and Gray (1926) found it necessary to 

 modify ionic concentrations or add veratrine in order to keep the 

 cilia beating. Aiello (1960) agreed that the lateral cilia of isolated 

 gills cease beating about one hour after removal from the animal; 

 he also found that if the branchial nerve on one side was cut close 

 to the visceral ganglion, the lateral cilia of the gill on that side 

 stopped after about an hour, while the cilia on the opposite gill 

 continued to beat. He was led to conclude that the cilia were 

 under control by activation, and, since serotonin increased the 

 rate of beat and was normally present in the gill, he suggested 

 that nerve activity caused the release of serotonin (probably as 

 a neurohormone) into the gill tissue as an activator of ciliary 

 movement. 



On the contrary. Nelson (1951, 1960) has described the 

 inhibitory control of lateral gill cilia of Ostrea virginica. The 

 lateral cilia in early transparent spat of this species can be seen to 

 cease their beating activity periodically for a itw seconds or more, 

 and then resume full activity again. This inhibition can be 

 destroyed by cutting the filaments from the gill axis, or by 

 application of chloretone. Nerves have been shown to run in 

 the gill filaments of Ostrea, and the inhibitory influence is probably 

 exerted by them. 



The control by activation in Mytiliis seems to be slow acting 

 and less direct than the inhibitory control of Ostrea, yet it should 

 be sufficient to reduce the activity of the cilia when not required, 

 e.g. when the shell is closed for long periods. It is possible that 

 control by activation is able to give a variation in the rate of beat 

 according to the amount of activator liberated, while inhibitory 

 control can only vary the activity by stopping the cilia for a longer 

 or shorter period. 



McDonald, Leisure and Lenneman (1927) believed that both 

 activation and inhibition are used in the control of the rate of 

 movement of frog pharynx cilia. They claim that stimulation of 

 the sympathetic nerves increased the ciliary activity, while it was 

 decreased by stimulation of the parasympathetic nerves. Although 

 others, e.g. Seo (1931) and Lucas (1935) have also found the 



