EXPERIMENTAL STUDY OF THE OYSTER GILL 



v^ 



which could not be attributed directly to changes in the surrounding medium. 

 Excluding the cases of accidental mechanical stimulation that may cause the contrac- 

 tion of the muscles in the gill tissue and result in a temporar}^ decrease in the velocity 

 or even in a complete stoppage of the current, the range of the fluctuations observed 

 in all the experiments varied with the temperature. It has been shown in a previous 

 paper (Galtsoff, 1928) that between 15° and 25° the fluctuations are small, ranging 

 from 4.4 to 5.9 per cent, but that they increase considerably both below and above 

 these temperatures. This means that the nearer we approach the temperature 

 limits of the ciliary activity the more irregular becomes the ciliary motion of the 

 gills. It must be borne in mind that the flow of water from the gill cavity is due 

 to the difference in pressure between the inside and the outside of the gills, and that 



TtMPtRATURE;" C 

 Fig. 5.— Effect of temperature on the rate o( flow oi water produced by the gills 



the velocity of the current is a function of a pressure drop between the two points. 

 The head pressure inside the gill cavity is maintained by the activity of the lateral 

 cilia and is dependent upon the rhythm and coordination of the ciliary motion along 

 the whole surface of the gill. 



The beat of the ciliary cell has two distinct phases — a very rapid forward or 

 effective stroke and a slow backward or regressive stroke. It has been shown by 

 Weiss (1909) and Gellhorn (1925) that the work performed by the cilium during one 

 phase is proportional to the cube of the velocity 



w=KV' . j,^,^^,i^i;:,(^, 



where Z is a constant, W is work, and V is velocity. The ability of the ciliated cells 

 to transport particles or produce a current depends on the difference in the velocities 



