THE LIFE-HISTORY AND HABITS OF THE PEARL OYSTER. 148 



of its bearing upon occasional pearl-formation. Many cases were noticed in our field 

 work where injuries had been effectively repaired, and it is significant that a number 

 of these were found on the Periya Paar Kerrai during March, 1903, immediately after 

 the time when we have evidence that Rays {Trygon uarnah) were feeding on the 

 bank and had crunched up many shells. Some of the oysters we found showed that 

 fragments of the ventral margin had been broken oft" others that the anterior or the 

 posterior " ear" had been smashed all had been repaired more or less perfectlv so as 

 to enclose the animal and enable the valves to function. 



To ascertain the extent and rapidity of the process of repair, a number of 

 experiments were made both on the pearl banks and at Galle. The following give 

 the details of a few typical cases : 



(a.) During the removal of oysters from the " Serendib " at Galle in April, 1902, a 

 2^-year old oyster had a large semi-circular fragment broken from the right valve. 

 The oyster remained for the next 26 days suspended in a wire-net cage from one of 

 the buoys in the bay. On May 9th, when brought into the laboratory, the gap was 

 mended completely and an additional marginal growth of 1 "4 to 2 millims. had formed. 

 The only departure noticeable from the original condition was that neither of the two 

 involved radial bands of colour had been continued in the repaired area, the pigment 

 being spread out instead in a diffused manner. 



(b.) In February, 1903, a number of oysters from the Cheval Paar were purposelv 

 damaged in various ways. When examined on the 23rd, 8 days later, they all showed 

 extensive repair. In one case 5f millims. of new shell had been added at the damaged 

 spot, and in two others 3^ millims. 



(c.) This was another oyster which had a piece fully 15 millims. in vertical depth 

 removed from the right valve on February 1 5th. In 9 days a fresh growth, measuring 

 7 millims. in depth, had formed, while by March 8th the whole of the damage was 

 made good by a further growth of 8 millims., so that within 21 days a total growth 

 of 15 millims. depth of new shell had taken place. 



(d.) Even more rapid repair was shown by some oysters damaged on February 27th, 

 due possibly to the fact that they were suspended in the purest sea-water on the 

 banks for the whole period of the experiment, whereas (b.) and (c.) above were kept 

 in muddy water off Chilavaturai for several days. The growth shown in (r>.) was 

 very uniform, and the damage was completely repaired in all cases. Of three 

 photographed on March 8th (two are shown in fig. 46) : 



No. 1 showed 9 millims. of new solid shell, 12 millims. including the "fingers," 

 9 7 1 '3 



1 > " ) > ' 11 1 ) 1 1 L " 11 11 11 11 



3 7 A 1 2 



>s . ii '2 " " >> " " >> u 



a surprising growth for 9 days. The colours of the new shell were very brilliant in 

 these cases, rich brown-red and bright yellow. 



