264 FIJI ISLANDS. 



Professor Semper of Wurzburg has examined the breathing 

 apparatus of the Cocoanut Crab {Birgus latrd), and finds * that 

 a large cavity on the back, commonly called the gill cavity, has 

 the function of a true lung. By means of blood-vessels in its 

 walls the animal breathes air directly. This cavity has been 

 commonly said to contain water, by which the animal was 

 supposed to moisten its gills, in order that it might breathe 

 through them alone. The breathing by the gills when on 

 land is considered by Semper as secondary. Similarly, the 

 gill cavity acts as a true lung in other Land Crabs. 



At Kandavu I had an opportunity of visiting the outer 

 margin of a barrier reef It was one of the reefs stretching 

 across the mouth of Ngaloa Bay. As it is approached from 

 behind in a boat, and viewed from sea level, nothing is visible 

 of the reef itself at a distance but a line of small detached 

 masses of rock which appear here and there, standing out 

 dark against the horizon. As the waves approach successively 

 the different portions of the reef, their crests are seen rising 

 dark above the reef-line. Then as they break against the 

 margin the isolated rock-masses show out in relief against the 

 white background of foam. 



As the reef is approached more closely, the water becomes 

 shallower, and assumes a yellow tinge, caused by the light 

 reflected from the growing corals. The boat now requires to 

 be steered with care along a zigzag path between coral patches, 

 and at last grates on the growing coral as the water shallows 

 rapidly towards the margin of the reef, and it becomes neces- 

 sary to wade in order to proceed further. 



It is in the shallow sheltered water, inside the actual edge 

 of the barrier, that the finest and best grown specimens of 

 the corals are to be found. The tufts, bushes, and rounded 

 masses of the various corals are to be seen growing here 

 in abundance, but scattered over the area, with plenty of 

 more or less barren interspaces in the "coral plantation," as 

 Dana terms it. The various forms of the spongy tissued Madre- 

 poras are the characteristic feature in these Fijian reefs, there 

 being no less than 26 species of Madrepora known from Fiji. 



The outer margin of the reef is raised above the level of the 

 coral plantation in the still waters within ; thus the water on it 

 is very shallow at low tide, and it is often laid dry. At Ngaloa 

 Bay the barrier reef springs from the fringing reef, running out 

 from the coast across the mouth of the bay. Its elevated 

 margin was not more than 20 to 30 yards wide. There is an 

 elevated strip of about this width stretching all along the reef ; 



* " Ueber die Lunge von Birgus latro." Zeitschrift fiir Wiss. Zoologie, 

 1878, s. 282. 



