272 THE GREAT BARRIER REEF. 



The researches that have been already conducted by European and American naturalists, 

 with relation to the commercial 03'sters of the northern hemisphere, have elicited the fact that 

 the fertilisation and development of the oyster brood or spat proceeds in each case upon a 

 distinct plan. In the case of the most familiar European type, Ostrca cdiilis, represented by the 

 far-famed British native, and the variety so extensively cultivated on the coast of France, the 

 propagation of the species is accompanied by a condition in which the oyster is unfit for 

 consumption, and is prohibited to be sold. This is occasioned through the circumstance that the 

 parent oyster nurses or incubates its brood within the pallial or mantle cavity, throughout the 

 early stages of its development, and does not liberate it until the shells of the young oysters are 

 fully formed. An oyster eaten during the later portion of the breeding season appears to be 

 full of sand or grit, this being due to the presence of millions of minute shell-bearing embryos. 

 By oyster dealers at home, two distinct spawning conditions of the oyster are recognised : 

 the one, when the embryos contained within the mantle chamber of the parent are white and 

 colourless, being devoid of shells, is designated the "white sickness." The later stage, when, the 

 shells being formed, a grey or blackish tint is imparted to the entire mass, is known as the "black 

 sickness." The close or spawning season of the ordinary European oyster, Ostrca ediilis, extends 

 throughout the summer, from May to September, and is popularly defined as coincident with 

 those months in which the letter "r" is absent. 



The fecundation of the ova of the European oyster necessarily takes place within the 

 mantle cavity or brood-chambers of the female. The fertilising agent or milt of the male is 

 discharged into the water, and thence it is transferred and brought into contact with the 

 mature ova, by the ciliary currents that exercise the ordinary respiratory, and food-purveying, 

 functions in the female mollusc. This plan of propagation was until within recent years supposed 

 to apply to all descriptions of oysters. Investigations associated with the reproductive phenomena 

 of the American commercial oyster, Ostrca virginiana, failed, however, to discover any trace of 

 the brood or spat within the mantle-cavity of the breeding oyster, and it was ultimately demon- 

 strated by Dr. Brooks (1880) that both the ova and milt were simultaneously discharged into 

 the water in their mature condition, and, fertilisation being there effected, that the entire develop- 

 ment of the embryo took place independentl}' of the parent. Such being the case, the artificial 

 propagation of the species by the commingling in sea water of the matured sexual elements was 

 considered feasible, and was successfully accomplished by the above-named authority. In the 

 case of the typical European oyster, Ostrca edttlis, such a method of artificial propagation is not 

 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 large 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 1882, that the small 

 Portuguese oyster, Ostrca angulata exhibits developmental phenomena which coincide essentially 



