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X. — On the Structure of Suberites domuncula, Olivi (0. S.), together with a 

 Note on peculiar Capsules found on the surface of Spongelia. By J. 

 Arthur Thomson. (Plates XVI., XVII.) 



(Read 7th June 1886.) 



Part I. 



The sponge Suberites domuncula attracted the attention of the Italian 

 naturalist Olivi* almost a hundred years ago, but was on account of its firm 

 india-rubber like consistency erroneously regarded as an Alcyonium. Beyond 

 the general diagnosis of NARDot who erected the genus Suberites, the struc- 

 ture of the sponge has, I believe, remained virtually unknown. Not for this 

 reason, however, but because the Monaxonia in general, of which Suberites is 

 an example, are still for the most part but little known, Prof. F. E. Schulze 

 of Berlin was good enough to ask me last winter to investigate the structure 

 of this sponge. To him, therefore — perhaps the greatest living authority on 

 the subject — I may be allowed to express my gratitude for the hospitable 

 reception with which he welcomed a stranger to his laboratory, and for the 

 constant interest and assistance with which he encouraged my work. That I 

 have not succeeded in giving a perfect elucidation of the structure is largely 

 due to the same cause which has kept it for so long almost wholly unknown. 

 The crowded siliceous spicules, the compact consistence, the smallness of the 

 ciliated chambers, make the histological analysis somewhat difficult. Such 

 gaps as exist in my investigation I hope to be able to fill up by the study of 

 related forms, and have with that end begun the study of Suberites mana. 



Suberites domuncula is found covering the outside of a sea-snail shell, 

 inhabited by a hermit crab. The change of position thus secured for the 

 sponge is an obvious advantage of this commensalism, while the hermit- 

 crab on the other hand is very effectively masked. Numerous polypes are also 

 found embedded in the sponge. In none of the forms which I had the oppor- 

 tunity of examining was the hermit crab present, and in all the limy shell was 

 to a greater or less extent eaten away, leaving in one instance only the apex. 

 How the lime is precisely affected I was not able to discover. The cavity 

 remaining after the shell has gone leaves a wide coiled canal, which will 

 doubtless aid in the irrigation of the compact mass. 



My material was obtained from the Berlin Aquarium, and after careful 

 dehydration, was stained (generally with alum carmine or hematoxylin), and 

 * Bronn's Klassen und Ordnungen, Vosmaer " Porifera," p. 33, t i&*&, P- 332. 



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