2 76 THE GREAT BARRIER REEF. 



a posterior passage and apertures, which correspond respectively with the throat and mouth, 

 and the intestine and vent. The shells make their appearance on the surface of the body, 

 and gradually increase in size until they enclose the entire animal. Simultaneously with these 

 metamorphoses a disc, covered with powerful vibratile cilia, has developed at the anterior ex- 

 tremity, with the assistance of which the embryo oyster can propel itself vigorously through 

 the water. "As the shells grow larger and heavier, the little oyster becomes less capable of 

 sustaining itself in the water, and finally sinks to the bottom. This is a crucial epoch in the 

 mollusc's existence. Should it settle upon a rock, shell, or other clean, hard substance, it 

 attaches itself to it, and its life is assured ; but should it, on the contrar}', light upon soft mud, 

 sand, or other material to which it cannot adhere, it inevitably perishes. The proportion 

 of )'oung 03'sters that find a secure anchorage, in comparison with the vast numbers that are 

 devoured, or become literally lost at sea, is necessarily infinitesimal." 



The time taken by the embryo of the Australian oyster to pass through the series of meta- 

 morphoses enumerated, and to arrive at the attached or sedentary state, has been found by the 

 author, under favourable conditions, to average four days, two out of these elapsing before the 

 shells become conspicuously apparent. 



Within from eighteen months to three years from the date of its birth, the embryo becomes a 

 marketable oyster, measuring the standard two inches in its longest diameter. Such, however, is 

 the precocity of the species that oyster brood, not more than three months old, and but half an 

 inch in diameter, was found, in association with the foregoing embryological investigations, to be 

 laden with fully-matured ova and milt. 



Some further experiments that were conducted, in the course of the foregoing enquiry, 

 with the object of ascertaining the influence of water of varying density, as in time of floods, 

 upon this embryonic oyster brood, have been referred to on page 258. Among the practical 

 results suggested, in connection with the foregoing embryological data, is the feasibilit)' of 

 fertilising, and artificially propagating, the embryos of Ostrea glomerata, in numbers largely- in 

 excess of what is accomplished in a state of nature. In Europe, where the demand is so 

 much in excess of the supply, and the market prices are consequently high, and also in 

 America, much attention is being given to the problem of thus successfully cultivating oysters 

 from their earliest embryonic state. By such time as this supply and demand shall be 

 equivalently balanced in the Australian market, a resort to methods of artificial fertilisation and 

 propagation may be found profitable. 



DETAILS OF AREAS RESERVED OR LEASED FOR OYSTER CULTURE IN 

 QUEENSLAND WATERS, WITH RETURN OF QUANTITIES AND VALUE OF 

 OYSTERS IMPORTED. 



The areas devoted to the industry of oyster culture in Queensland waters fall under the three 



