THE SPA-WNING OF OYSTERS. 233 



ihg from the border of the mantle have no optical power what- 

 ever ■ but, be that as it may, the oyster has a power of knowing 

 the light from the dark. 



As 'is well known, there is a period every year during 

 which the oyster- is not fished; and the reason why our English 

 oyster-beds have not been ruined or exhausted by over fishing 

 arises, among other causes, from there being a definite close-time 

 assigned to the breeding of the mollusc. It would be well if 

 the larger varieties of sea produce were equally protected ; for 

 it is sickening to observe the countless numbers of unseasonable 

 fish that are from time to time brought to Billingsgate and 

 other markets, and greedily purchased. The fact that oysters 

 are supplied only during certain months in the ye^, and that 

 the public have a general corresponding notion that they are 

 totally unfit for food during May, June, July, and August (those 

 four wretched months which have not the letter "r" in their 

 names), has been greatly in their favour. Had there been no 

 period of rest, it is almost certain that oysters would long ago 

 — I allude to the days when there was no system of cultivation 

 — have become extinct. 



Oysters begin to sicken about the end of April, so that it 

 is well that their grand rest commences in May. The shedding 

 of the spawn continues during the whole of the hot months — 

 not but that during that period there may be found supplies 

 of healthy oysters, but, as a general rule, it is better that there 

 should be a total cessation of the trade during the summer 

 season, because were the beds disturbed by a search for the 

 healthy oysters the spawn would be scattered and destroyed. 



Oysters do not leave their ova, like many other marine 

 creatures, but incubate them in the folds of their mantle, and 

 among the laminse of their lungs. There the ova remain 

 surrounded by mucous matter, which is necessary to their de- 

 velopment, and within which they pass through the embryo state. 

 •The mass of ova, or "spat" as it is familiarly called, undergoes 

 various changes in its colour, meanwhile losing its fluidity. 

 This state indicates, it has been said, the near termination of 

 the development and the sending forth of the embryo to an inde- 

 pendent existence, for by this time the young oysters can live 

 without the protection of the maternal organs. An eminent 

 French pisciculturist says that the animated matter escaping 

 from the adults on breeding-banks _ is like a thick mist being 

 dispersed by the winds — the spat is so scattered by the waves 



