180 ANATOMY AND LIFE HISTORY OF MOLLUSCA. 



but grows fast. If it has not some object to fasten to, it sinks to 

 the bottom. There it may find the living and dead shells of its 

 relatives, or a rock or other shells, and there it will grow. It is 

 not uncommon to find nearly a hundred small " spat " on one 

 oyster shell. It is then that oyster cultivators collect them and 

 lay them in convenient places to fatten. Without artificial 

 assistance there can be no doubt that the great mass of oyster 

 ova perish. 



Many observers have asserted that the ova are fertilized within 

 the ovary, and are afterwards nursed in the folds of the mantle. 

 Dr. Brooks has proved that this is not true of the American 

 oyster (0. virginiana).* Up to a very recent period all my 

 observations tended to confirm this. In my "Fish and Fisheries 

 of New South Wales/' published in 1882, I wrote as follows 

 (p. 114) : — "I have carefully examined many ripe female oysters, 

 and never could find any embryos on the mantle. It is probable 

 that the egg is discharged into the water to be fertilized, where 

 in oyster-beds and amidst its own species it easily may meet with 

 a male cell. If, however, it does not meet with such, the ova are 

 rapidly destroyed by sea water." 



In these observations I am now convinced that I have been 

 completely wrong, and I hasten to correct the erroneous conclusions 

 founded on them. My error arose from the kind of oysters I 

 selected for experiment being those in which the ova was barely 

 ripe, with no young oysters in them except those which had been 

 obtained by artificial fertilization. Recently the experiments 

 were renewed, and investigations made upon oysters in which the 

 ovary seemed nearly empty. On submitting the gills of these to 

 microscopic examination, I found in the openings between the 

 filaments where the water comes into more immediate contact 

 with the blood, a number of young oysters, in fact in the same 

 position in which the young embryos are found in the Unio or 

 freshwater mussel. The whole of this portion of the branchial 

 filaments is richly furnished with cilia which keeps up a visible 

 current in the openings. In these the young oysters may be seen 

 hurried to and fro by the current, in every stage of development. 

 The majority had their shells, if not forming a complete valvular 

 investment, at least in an advanced state of development. Only 

 a few larvae in the veliger stage were perceived. The sight is a 

 most beautiful and interesting one, and may be witnessed for 

 fully half-an-hour after the animal is dead. 



The life-history therefore of the Australian oyster is this. 

 When the ova have been fertilized they are segmented with 



*" Development of the American Oyster," by Dr. W. Brooks, p. 15. 

 Printed as an Appendix to the Report of the Commissioners of Fisheries 

 of Maryland, January, 1880, Annapolis, State Printers, 1880. 



