130 CEYLON PEARL OYSTER REPORT. 



fixation, locomotion, and possible migration or transplantation is so close and so 

 important that we shall give here the results of our experiments on the matter. 



Kelaart showed, in 1858, that the young pearl oyster can move from place to 

 place, can detach its byssus and can re-attach in a new spot. Sullivan Thomas, in 

 1886, added some fresh observations on young oysters, about |- inch in diameter, 

 which he found moved up the smooth side of a glass 4 inches in 8 or 9 minutes. 

 He also made some observations on the byssus, and found that a young oyster, 

 measuring 1^ inches in diameter, withstood steady tension measured with a spring- 

 balance till it reached 2f lbs., when the byssus came away at the root. He adds : 

 " I conclude that a pearl oyster is not likely to be dislodged by the force of wave 

 action or current, and that, if it moves, it moves voluntarily."* 



Some of our observations on the rapid movements of very young pearl oysters 

 much younger than those dealt with by Kelaart and Thomas and on the readiness 

 with which they detach and re-attach, were given in the "Narrative" (p. 68), and we 

 have many others, which, however, it is unnecessary to give in detail. But although 

 the very young are thus actively locomotive, it has been doubted, and may still be 

 doubted by some, whether the adult oyster is capable of movement, or even of 

 re-attaching, if the byssus be torn. Our observations settle this point definitely, as 

 the following examples show : 



A 2J years old pearl oyster, obtained from the Muttuvaratu Paar on April 11th, 1902, 

 had the byssus broken by being torn from its attachment to rock. Two days later it 

 was marked and suspended in a wire-net cage in Galle Harbour under observation. 

 After 3 days it was found to have re-attached to another oyster in the same cage. 

 On May 9th it was removed to a tank in the Biological Station, and the new byssus 

 was then found to be normal, stout-fibred, and of a bronze-green colour. It was then 

 torn across by force, thus breaking the byssal strands, and was placed in a small glass 

 dish sunk in the tank. On May 10th an inch and a half of sand was put over the 

 top of the oyster. On May 1 1th it had freed the ventral margin of the valves from the 

 sand, and appeared healthy. On May 12th the shells were half uncovered, and the 

 animal was breathing and feeding normally. On May 13th and 14th the animal still 

 lay unattached. On May 15th, at 8 a.m., the old byssus was still present; at 9 a.m. 

 the foot was protruded, and shortly after a new byssal strand had been formed attaching 

 the oyster to the side of the glass. The old byssus was still retained, but was ejected 

 during the night, as at 8 a.m., on May 16th, it lay just beyond the byssal sinus of 

 the shell, and two additional strands had been added to the new cable. The rest may 

 be quoted from the laboratory diary kept by Mr. Hornell : 



May 17 th, 8.10 a.m. The oyster had travelled 3^ inches during the night, sloughing 

 the 3 byssal strands, formed the night before, together with the common root. 

 The thrown-off byssus remained attached to the glass. At the place of second 

 re-attachment, 5 pale-coloured strands connected the oyster with the glass. 

 * ' Madras Journ, of Literature and Science ' for Session 1886-87. 



