2i6 THE GREAT BARRIER REEE. 



smallest shells, one or two of which crept from tlie upper and re-attached themselves to the 

 shaded under surface of an empty oyster-shell, upon which they had been placed. A specimen 

 in another instance removed itself for the space of a few inches before re-attaching itself by 

 its new byssus. Two of the smallest examples, about a quarter of an inch diameter, which 

 were temporarily kept in a wide-mouthed bottle, were observed to creep with the aid of 

 their slender protrusible feet a little distance up the side of the bottle, to which they then 

 made themselves secure by the secretion of a byssus. This byssus, or anchoring-cable, is 

 secreted a thread at a time. During its exudation it is of the consistence of liquid glue ; but 

 it rapidly hardens in the water. The byssus of living examples of the true pearl-shell, Mclea- 

 grina margaritifera, was, in all cases observed, whether young or old, of a glossy sea-green hue ; 

 the number of threads or strands of which the entire cable is composed are usually from thirty 

 to forty. It may be mentioned that the extemporised aquaria, represented by the large clam- 

 shells, in which the young pearl-shells were confined, were located on the hillside immediately 

 in front of the Residence. They were thus fully exposed to the action of the south-east 

 monsoon, which, at the period of the experiments conducted, August and September, blows 

 strongly and continuously. By this means the thorough oxygenation of the water in which 

 the shells were kept was constantly secured. The only additional precaution taken for the welfare 

 of the little Meleagrinae was the placing of a board over the top of the clam-shells to screen 

 the water, with its living contents, from the direct rays of the midday sun. 



The facts that were determined by the experimental culture of the young shell may be 

 thus summarised : i. It was conclusively demonstrated that the pearl-shell, in its 3'oung con- 

 dition at least, firmly attaches itself to submarine objects by means of a so-called byssus or 

 anchoring cable. 2. That, in the event of injury, the primary byssus could be ejected and a 

 new one secreted. This fact carried with it the demonstration that the animal was capable at 

 will of separating itself from its original fulcrum, and of re-attaching itself elsewhere. 3. Whilst 

 the young animals were found to possess the capacity of locomotion, such locomotion was shown 

 to be of a feeble character and but rarely exercised. In this respect the habits of the pearl-shell 

 were found to coincide, to a considerable extent, with those that have been observed of ordinary 

 mussels, genus Mytilus, and the typical wing-shells, genus Avicula. Active locomotive functions 

 similar to those of the scallop-shells, genus Pecten, and an allied type, genus Lima, — both of 

 which can transport themselves to considerable distances by the opening and closing of their 

 valves, — are certainly not possessed by the pearl-shell, Meleagrina margaritifera, and have been 

 incorrectly ascribed to it by divers and owners of shelling boats. 



The information gathered concerning the habits of the young pearl-shell was next ex- 

 tended to those of the more matured, and of adult, individuals. This was accomplished chiefly 

 through the acquirement of materials obtained in an excursion, made in the Q.G.S. Albatross, to 

 one of the most prolific shelling grounds in Torres Strait, lying west from Bado or Mulgrave 



