254 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
It is quite noticeable that 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 through 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 lowe 
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. 
Fig. 103. Plan of а part of the west edge of Inasmuch as these grow- 
Lixa reef. 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; chapeirdes 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 
reef. Low tide. 
middle. 
The anchor always brings up from the bottom blue calcareous mud ; 
