8G 



forming corals undoubtedly increase — as compared with others — 

 at a greatly augmented ratio, in consonance with their structure 

 and their individual conditions of environment. To arrive at an 

 exact knowledge of their specific peculiarities in this respect, 

 living coral masses must he selected and carefullv measured from 

 time to time, and their bearings recorded with reference to other 

 corals growing on the same reef. As an experimental step 

 towards the accomplishment of the investigations suggested, I 

 availed myself of the opportunity afforded at Thursdav Island, of 

 making a few observations regarding the dimensions and relative 

 ])roximit}^ of the coral on certain of the most easily accessible 

 reefs, and which observations may subserve as a basis for more 

 systematic investigations iji the same direction. In this manner 

 an isolated portion of the reef, on the extreme edge of Vivian 

 Point, Thursday Island, as exposed by the low spring tide early 

 in the month of June, was measured off, and the dimensions and 

 relative positions of the various descriptions of corals growing on 

 it carefully recorded. The substratum of thi:; isolated ])oint of 

 the reef consists of a dense mass of Porifes, which measures 19 

 feet in its largest diameter. The several descriptions growing 

 upon it, and whose dimensions Lave been taken, are referable to 

 the several genera — Madrepora, Pocillopora, MeancJrina, Mussa, 

 and 8ymplu/llia. An adjoining coral block is a gi'ey-green Asfrea, 

 measuring 8 feet 2 inches across its longest axis. A channel, exactly 

 2 feet wide in its narrowest point, separated these two coral blocks 

 at the date of measurement. A rough outline ])lan of the 

 positions and measurements recorded is herewith submitted. It 

 will be an easy task, with the aid of this plan, to ascertain from 

 time to time the extent to which the several coral masses have 

 enlarged their dimensions. The same system of registration is 

 capable of application on an extended scale, throughout consider- 

 able areas in the vicinitv of Thursday Island, and would be 

 productive of valuable results. The most unerring and 

 efficient assistant in mapping out the salient characters, 

 dimensions, and relative positions of coral growths is, no doubt, 

 the camera. This instrument was somewhat extensivelv utilised 



