OYSTERS AND OYSTER FISHERIES OF QUEENSLAND. 273 



with those of the American species, the ova being similarly discharged into the water, where they 

 are fertilised and developed independently of the parent. The artificial fertilisation of the ova of 

 this species, and the investigation of the more important embryological phases of this Portuguese 

 type, were also successfully carried out by the authority cited. 



The oysters of Australia, like those of the northern hemisphere, exhibit two distinct plans 

 of propagation. The commercial form indigenous to Tasmania and Victoria, but now so reduced 

 in numbers by exhaustive fishing as to be scarcely known in the market, cannot be distinguished 

 from the Ostrea ediilis of European waters, and it is usually associated by naturalists with the 

 same specific title, but is sometimes denominated the variety Angasi. The reproductive 

 phenomena of this oyster have been personally investigated by myself, and were found to 

 coincide precisely with those of its European congener, the embryos in like manner being fer- 

 tilised and developed within the mantle or pallial cavities of the parent. Similar phenomena 

 have also been found by me to obtain in the closely-allied New Zealand mud oyster, which is 

 also, apparently, a local variety only of the same species. 



The most important commercial oyster of Australia is undoubtedly the familiar rock oyster, 

 Ostrea glomcrata, of which Queensland enjoys the enviable position of producing the largest 

 supplies ; Moreton Bay and Wide Bay alone growing sufficient quantities not only for home con- 

 sumption but also for exportation to the neighbouring colonies. The method of propagation of 

 this oyster, to which I have paid some attention within the past few weeks, is, I find, in all 

 respects identical with that of the American commercial species, Ostrea virgiiiiaiia. The fertilisa- 

 tion of the ova is brought about by their coming in contact with the milt or sperm cells in the 

 open water, the young embryos being thus cast adrift and thrown upon their own resources from 

 the earliest period of their existence. The artificial propagation of this species by the abstraction 

 of the matured sexual elements, the ova and spermatozoa, and their admixture in a little sea- 

 water, may in consequence be easily effected, and yields a most interesting and instructive 

 embryological study. The method of procedure successfully adopted in accomplishing such 

 artificial propagation, and the more conspicuous metamorphoses through which the embryo passes 

 before assuming the parent form, may be described as follows : — 



The aid of a microscope with a magnifying power of about 200 diameters is, in the first 

 instance, indispensable for securing the most satisfactory results. On opening a number of 

 oysters, the cream-coloured, fat-like mass, near the hinge or joint of the bivalve shell, represents 

 the seat of the reproductive elements. Inserting a fine spatula in the midst of this mass, a small 

 portion may be abstracted, and spread out in a drop of sea-water, or in the natural juices of the 

 mollusc, on an ordinary glass slip. Placed under the microscope, the ova of the female will be 

 at once recognised by their ovate or pyriform contour, the separate ova having an average 

 diameter of the xoTrth part of an inch. The male elements, or spermatozoa, when abstracted and 

 similarly treated, present a widely different aspect. Its separate elements are so diminutive as to 



