412 



F. W. GAMBLE AND FREDERICK KEEBLR. 



3. Variations in the Constituent Patches 

 of a Colony. 



As we have ah-eady stated^ the colonies and their com- 

 poneut patches remain in their broad outlines constant day 

 by day. One colony figured on PI. 30, figs. 1, 2, and under 

 observation throughout July and August, 1902, presented 

 the same outline on the last day as on the first. Never- 

 theless variations occur. Sudden changes follow the appli- 

 cation of a sudden disturbance. Daily aud lunar periodic 



Text-fig. 3. — The two sketches show ilie influence of vibration on a 

 patch of Con vol ut a. Tlie left-hand ligure sliows tlie patcli at 

 rest,; the right-hand figure tlie result of tapping gently, and is 

 taken five minutes after the former. The pencil gives the 

 scale. (From photographs.) 



changes are also noticeable. Of these Ave now give some 

 account. 



Von Graff (1891) had noticed that by tapping the sand 

 in the neighbourhood of a patch the disappearance of 

 Convoluta into the sand could be almost instantaneously 

 effected. Text-fig. 3 is from a photograph illustrating this 

 phenomenon. The interval between the two figures was 

 in this case five minutes; but much shorter intervals, a 

 minute or loss, suffice. The depth to which Convoluta 

 descends is difficult to determine, but we may say it is such 



