314 G. p. BIDDER 



Note 2. Kegulation of the Size of the Osculum. 



In two examples of Leucandra aspera (one with an 

 iris-like oscular sphincter) I cut off the oscular end for preserva- 

 tion, and observed that the aperture contracted to one-third 

 of its normal diameter. Mechanical stimulation failed to induce 

 further contraction. 



There was more than once evidence that the oscular aperture 

 contracted when the current through it grew feebler, though 

 the contraction was not sufficient to keep from diminution 

 either the oscular velocity or the length of the jet. In a 

 Leucaltis, observed over 24 days, the osculum contracted 

 to half its original diameter, while the length of the jet dimin- 

 ished from 18 cm. to 1 cm. I give this series of measurements, 

 which shows also that when the current recovered (probably 

 with a lower temperature) the osculum widened again. 



20, 21, 22, 23, 29, 29, 30, 30, 30, 31 

 •20 -205 -20 -20 -17 -16 -18 -18 -18 — 



6-5 6-7 6-2 4-4 -9 -5 1-6 1-0 -5 -7 



Parker found in Stylotella (' Journ. Exp. Zool.', 8, p. 784) 

 that the oscula close when the external water is still ; this may 

 be called 'Parker's reaction'. In Leucandra and Leu- 

 caltis it is shown by the sphincter of the osculum being 

 inhibited from contraction by the movement of water over its 

 internal surface. If the reaction is such that there is neither 

 contraction nor relaxation in response to the velocity character- 

 istic of the species (Note 5 (12)) the optimum osculum will be 

 maintained at all stages of growth. 



Note 3. Delivery of Water and Secretion of 

 Lime. 

 In the Leucandra aspera of Text-fig. 1 , taking the mean 

 oscular velocity at 8-5 cm. per second (see Note 1), the area of 

 the osculum being 0-031 sq. cm., the delivery per second was 

 0-2G c.cm., or 16 c.cm. per minute ; that is -9 litre an hour, 

 90 litres in 4 days, and a ton in 45 days (see Note 61 



