17(1 CEYLON PEAEL OYSTER REPORT. 



Heteropsammia michclini, Ed. and H., kindly identified for me by Mr. J. Stanley 

 Gardiner, The specimens were all in a highly contracted condition, and most of 

 them showed hardly any portion at all of the introvert, but Mr. Gardiner was able 

 to place at my disposal a collection of the same species, made off Madras by 

 Ramunni K. Menon, a former pupil of mine. The external appearance of one or 

 two of these is shown in Plate I., figs. 1 and 2. 



Sluiter's material enabled him to confirm Bouvier's view that the original home 

 of the Aspidosiphon is a Gasteropod shell on which the young coral comes to rest. 

 This shell becomes gradually embedded in the stony framework of the Heteropsammia. 

 The smallest of Sluiter's examples showed the small Gasteropod shell, belonging to 

 the genera Cerithium, Natica, and others, only partly overgrown and the young 

 Gephyrean living wholly Avithin the shell. In older stages the corallum spreads until 

 it reaches and finally grows past the mouth of the shell, but the shell, according to 

 Sluiter, is not absorbed, but can still be detected if carefully sought for. 



On the body, mostly towards the posterior end and therefore, as the animal lies 

 most remote from the opening, of several of Professor Herdman's examples, were a 

 number of minute molluscs which Mr. Edgar A. Smith has kindly examined, and he 

 is of the opinion that they might range with the genus Mysella of Angas. The 

 animals are, however, so minute, that their exact determination is a matter of great 

 difficulty. 



These were so closely adpressed to the skin of the Aspidosiphon as to indent it, 

 appearing as little pearls set in a matrix. The advantage they obtained by taking up 

 such a position is not very evident, but there they were, and as far as one could judge 

 they were, until Professor Herdman dropped them into his collecting jar, nourishing. 



The whole question of such commensalism as exists between the Aspidosiphon and 

 the coral is an interesting one. Commensalism is usually looked upon as conferring 

 some mutual advantage on the contracting parties, and one or the other of these 

 usually seeks the other out. But in the case in question the mutual advantage is far 

 to seek. It can hardly help the coral to have a large portion of its base burrowed by 

 a spacious canal, but the fact that the Gephyrean pulls the otherwise immovable 

 coral about may be, and probably is, an advantage to the Coelenterate. On the other 

 hand, the Gephyrean gains protection and a home more spacious than the Gasteropod 

 shell affords. The Aspidosiphon can hardly find, or attract the larval coral to come 

 to rest on its burrowed shell, and it is unlikely that the larva is especially on the 

 outlook for such shells as are inhabited by Gephyrea, It seems more probable that 

 the Aspidosiphon may select for its home a Mollusc shell which already bears a young 

 coral, but the whole matter seems to demand more careful study. It is certainly 

 remarkable that three distinct genera of coral, each with but one species, should be 

 inhabited by three distinct species of Aspidosiphon, and that neither commensal has 

 hitherto been found apart from the other. 



The specimens were obtained at various localities in the Gulf of Manaar (Stns. I., 



