14 



possible, chiefly on account of the fact that the embryos are matured within the brood-chambers of the 

 parent in a fluid medium, containing a hirge proportion of albuminous matter that cannot be artificially 

 produced. Following upon the discovery of Dr. Brooks in connection with the American oyster, it was 

 demonstrated by M. Bouchon-Brandeley, in the year 18S2, that the small Poituguese oyster, Ostrea 

 angulata, exhibited developmental phenomena which coincided essentially 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 lype, were also successfully carried out by 

 the authority cited. 



" The oysters of Australia, like these of the Northern hemisphere, oxhibit 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 iu the market, cannot be distinguished from the Ostrea edulis 

 of European waters, and is usually associated by naturalists with the same specific title, but is sometimes 

 denominated the variety Angasi of the same type. 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 mauner being fertilised and developed within the mantle or pallial cavities of the 

 parent, similar phenomena have also been found by me to obtain in association with the closely allied 

 New Zealand mud oyster, and 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 

 glomerata, of which Queensland enjoys the enviable po.sition of producing the largest supplies ; Moreton 

 Bay and Wide Bay alone growing sufiicient quantities not only for home consumption 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 virgineana. The fertilisation 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 sta wattr, may in consequence bo eas'ly effected, and yields a most interesting and 

 instructive embryological study. The method of procedure successfully adopted in accomplishmg 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 the natural juices of the mollusc, on an ordinary glass slip. Placed 

 under the microscope, the ova or germs of the female oyster will be at once recognised by their ovate or 

 pyriform contour, the separate ova having an avernge diameter of the -j-Jo^^^ P''"'* o^ ^^ inch. The male 

 elements or spermatozoa, when abstracted and similarly treated, present a widely different aspect. Its 

 separate elements are so diminutive as to appear as minute granules only under the same magnification, 

 and a considerably higher amplification is requisite to illustrate their individual structure. This is then 

 shown to consist of a minute bulbous head and an exceedingly slender flexible hair-like tail, the pro- 

 portions between the two being much the same as that of the head and shank of an ordinary pin. After 

 a little experience it will be found easy to distinguish the comparatively coarse granular ova from the 

 cloudy masses of spermatozoa, when placed on the glass slip, with the aid only of an ordinary pocket 

 lens or even the unassisted vision. The assistance of the microscope is, however, desirable to insure the 

 most favourable results, and is altogether indispensable for tracing the further development of the 

 embroyos. In many instances it will be found, what can be recognized only with the microsope, that the 

 ova or spermatozoa, are not sufficiently matured, or, in the case of oysters purchased in the market, have 

 become deteriorated by isolation from their native element for too long a period to permit of perfect 

 fertilisation. All conditions being satisfactory, the ova under the microscope should present a clean and 

 evenly rounded outline, while the vitality of the spermatozoa should be manifested by their active 

 oscillating and vibratory movements. Should the sperm cells fail to exhibit this vitality, their admixture 

 with the ova will prove of no avail. 



In practice it will be found that the number of oysters containing the female elements or ova is 

 grejitly in excess of those producing the milt or sperm cells, the average proportion associated with many 

 hundred examples recently examined being one male to six or seven females. The small quantity of milt 

 that is required to fertilise a very large num.ber of ova satisfactorily explains Nature's economy in this 

 direction. No peculiarities of external structure exist, so far as I have been able to ascertain, that 

 permit of distinguishing between the male and female oyster before it is opened. Healthily matured 

 milt and ova having been successfully obtained, portions of each, the ova predominating, may be mixed 

 in a watch-glass half full of sea water, and well stirred together. The ova, being he;ivier, will soon sink 

 to the bottom, leaving the spermatozoa diffused as a cloud through the water. After an interval of ten 

 minutes the lop water may be poured off or withdrawn with a pipette and fresh supplied, and any 

 fragments of lacerated tissue or tufts of immature milt be removed with a needle ; these, if left, will 

 decay and pollute the water. The pouring-off process should be repeated until the to]) water is quite 

 clear and the bottom consists entirely of fertilised ova. If a small drop of water containing the mingled 

 mUt and ova is examined under the microscope at short intervals, some remarkable changes in the form 

 and structure of the ova will soon be observed. 



Almost immediately following upon the admixture of the two elements it will be found that the 

 sperm cells are adhering in numbers by their dilated heads to the delicate capsular investments or vitelline 

 membranes of the ova, and communic^ating to many of them, through the vigrous vibrations of their 

 tail-like prolongations, a distinct oscillatory motion. It may also be observed that through the 

 aperture of the narrower end of the capsule, known as the micropyle, several of the sperm cells have 

 effected an entrance, and have been brought into direct contact with the body of the ovum. The fusion 

 between the two elements that then takes place is not easy to trace, but the results arising from the 

 union are speedily manifested. The ovum prior to fertilisation was distinguished by the presence of 

 a central clear area with a contained nodular structure, the two representing what are distinguished 



technically 



