I I 2 BREEDING OF THE OYSTER chap. 



ranks. Cliona, a parasitic sponge, bores in between the layers 

 of the oyster's shell, pitting them with tiny holes (corresponding 

 to its oscula), and disturbing the inmate, who has constantly to 

 construct new layers of shell from the inside. Weed, annelids, 

 ' blubber,' shifting sand or mud, sewage or any poisoning of the 

 water, are seriously harmful to the oyster's best interests. A 

 very severe winter is often the cause of wholesale destruction in 

 the beds. According to the Dail.T/ Neios of 26th March 1891, 

 the Whitstable oyster companies lost property to the value of 

 £30,000 in the exceptionally cold winter of 1890-91, when, on 

 the coast of Kent, the surface temperature of the sea sank below 

 32°, and the advancing tide pushed a small ice-floe before it. 

 Two million oysters were laid down in one week of the following 

 spring, to make up for the loss. During the severe winter of 

 1892-93 extraordinary efforts were made at Hayling I. to protect 

 the oysters from the frost. Twenty million oysters were placed 

 in ponds for the winter, and a steam-engine was for days 

 employed to keep the ponds thawed and supplied with water, 

 while large coal and coke fires were kept burning at the edge of 

 the ponds.^ On the other hand, the unusually warm and sunny 

 summer of 1893 is said to have resulted in the finest fall of spat 

 known in Whitstable for fifty years.^ 



The reproductive activity of the oyster is supposed to com- 

 mence about the third year. Careful research has shown ^ that 

 the sexes in the English oyster are not separate, but that each 

 individual is male as well as female, producing spermatozoa as 

 well as ova in the same gland. Here, however, two divergent 

 views appear. Some authorities hold that the oyster does not 

 fecundate its own eggs, but that this operation is performed by 

 spermatozoa emitted by other specimens. It is believed that, 

 in each individual, the spermatozoa arrive at matmdty first, and 

 that the ova are not produced until after the spermatozoa have 

 been emitted; thus the oyster is first male and then female, 

 morphologically hermaphrodite, but physiologically unisexual. 

 Others are of opinion that the oyster does fecundate its own 

 eggs, ova being first produced, and passed into the infrabranchial 

 chamber — the 'white-sick' stage — and then, after an interval, 



^ St. James's Gazette, 6tli January, 189.3. 



" Also at Arcachon (W. A. Herdman, Nature, 1893, p. 269). 



^ See especially Hoek, Tijdschr. Ned. Dierlc. Vercen, Suppl. Deal, i. 1883. 



