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BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



It is quite noticeable tliat these growing projections lean with some 

 uniformity in a certain direction. These directions, however, are not 

 always the same. The most marked cases I noted were in east-west 

 channels, where most of these points leaned toward the west. I suppose 

 these forms to be due in some way to the influence upon the growing 

 polyps of the movement of the tidal currents thi'ough the channels. 



The forms of the growing portions as seen in plan are much more 

 varied ; indeed, there seems to be no limit to the shapes of these masses 



below a certain level. This 

 certain level I take to be the 

 depth at which the polyps 

 are injuriously affected by any 

 agency whatever at the low«= 

 est spring tides. 



These growing portions 

 start out from the larger reefs 

 like long knotted fingers, or 

 rise like solitary stumps from 

 the bottoms of the channels. 

 The following are plans of 

 some of them. 



Inasmuch as these grow- 

 ing portions of the reef are 

 in the deep channels that traverse it, the channels themselves vary 

 greatly in outlines — width and depth. Some of the measurements 



may here be given : 



Channel 300 metres wide, 

 8 metres deep at low tide ; 

 a few isolated coral masses 

 rising from the bottom. 



Channel 80 metres wide, 

 3 metres deep. 



Channel 85 metres wide, 

 8 metres deep; with 

 chapeirao. 



Channel 65 metres wide, 9 metres deep ; chapeiroes at the margins. 

 The bottoms of these channels are as nearly flat as may be ; the depth 

 measurements next to the walls are but little different from those in the 

 middle. 



The anchor always brings up from the bottom blue calcareous mud ; 



Fig. 103. 



Plan of a part of tlie west edge of 

 Lixa reef. 



Fig. 104. 



Form of one of the channels of Lixa 

 reef. Low tide. 



