OYSTER CULTURE EXPERIMENTS IN LOUISIANA. 23 



It was observed that the few upper valves still adherent to the 

 shells were perforated by small holes, and as the gasteropod Purpura^ 

 locally known as the " borer " or " snail," was abundant on the stakes 

 marking the beds it was at once suspected to be the cause of the 

 mortality. To test this hypothesis three boxes were constructed of 

 one-fourth inch wire screening and planted on the beds on April IT, 

 1907; one, closed, containing both shells and borers; one, closed, con- 

 taining shells alone ; and the third, open, with shells only. On June 

 26 the contents of the boxes were examined with the following results : 

 In the open box 18 per cent of the shells bore spat, of which several 

 were dead, and there were 5 borers besides several fishes and crabs. 

 In the closed box, containing shells and 12 borers, but 2 per cent of 

 the shells bore live spat, and these were concealed either under the 

 shells or by marine growths. In the closed box without borers 60 

 per cent of the shells bore live spat, averaging two to the shell. This 

 box contained when taken up 14 very small borers which had evi- 

 dently entered through the mesh. 



On June 26 two closed boxes were planted, one with clean shells 

 and 9 large borers, and the other containing shells bearing spat from 

 one-half to three-fourths inch long, but with no borers. ^\Tien 

 taken up on September 1 the shells in the first box were devoid of 

 spat of appreciable size, the large borers were dead, and there were 

 no small ones. In the other box there were 17 live borers between 

 three-eighths and 1\ inches long which must have crawled through 

 the mesh when quite small ; there were no dead borers, but 2 per cent 

 of the spat had survived and all of the upper valves remaining 

 attached showed the small perforation made by this enemy. 



The brood oysters planted in January, 1906, when they were be- 

 tween 2 and 3 inches long, at no time showed any greater mortality 

 than was to be expected from the mere act of transplanting, and this 

 fact in connection with the experiments just recounted shows without 

 much doubt that the failure to obtain results from planting shells 

 was due, not to the quality of the water, per se, but to the destructive 

 habits of the borer. The largest spat killed was less than 1\ inches 

 in length, and it is safe to assume that seed oysters 2 inches long 

 and probably as small as 1^ inches will be immune. 



The borers lay their eggs in red or purple leathery capsules about 

 one-half inch long, attached in dense clusters to shells, stakes, and 

 other fixed bodies in the water. The capsules are demicylinders, 

 usually more or less curved toward the convex surface and with 

 flattened or slightly convex free ends. Each capsule contains several 

 eggs and the young snails escape through holes less than one-fiftieth 

 of an inch in diameter, which they cut in the free end of the capsule. 



34455—10 4 



