316 A. EARLAND ON CYMBALOPORA BVLLOIDES 



The walls of the " float " chamber are of calcite of the most 

 delicate transparency and thinness, more like the film of a soap 

 bubble than any rhizopod shell, and it is quite devoid of all per- 

 forations except the tube already alluded to. Now this is a very 

 extraordinary feature, and I think quite unique. Hitherto the 

 calcite shell has been regarded as essentially and typically per- 

 forate, and the aragonite (or conchite, according to Chapman) 

 shell essentially imperforate. But here we have a typically and 

 coarsely perforated foram possessing an internal chamber at 

 variance with what has been considered the essential feature of 

 its group. Such a radical departure must have an adequate 

 ■reason to account for it, but what that reason may be is not very 

 apparent. It is, however, permissible to put forward a theory to 

 account for its presence, and in my opinion this inner chamber 

 is neither a breeding chamber nor a body chamber, but a " float." 

 No specimens which I have examined show any trace of sarcode 

 on the interior surface, which is invariably smooth and shiny ; 

 while the exterior surface, in common with the walls of the 

 balloon chamber, are frequently covered with patches of dried 

 sarcode. The absence of perforations would be a valuable feature 

 in a chamber designed to hold air or gas ; but, on the other hand, 

 if the " float " were to contain sarcode, the contents would be 

 practically isolated from the remainder of the animal, which could 

 hardly be beneficial. 



What purpose is served by the tube ? Possibly the animal has 

 the power of increasing or depleting the supply of gas in the 

 chamber so as to modify its specific gravity, and so travel from 

 the bottom to the surface and vice versa. 



It is not easy to understand how such a striking feature, and 

 one by no means diflicult to detect, can have been overlooked by 

 such careful and skilled observers as Moebius and Brady, to 

 mention onlv those who have written of the form in detail. 

 There is no doubt that both of these writers were ignorant of its 

 existence, for they both mention specifically that the final balloon 

 chamber is single. Yet they must both have been within a hair's 

 breadth of detecting its presence, for there are distinct though 

 faint indications of its presence in their illustrations of the form. 

 The figures in Moebius' w^ork, drawn by himself, include one 

 (PI. X., fig. 9) showing an idealised optical section of the 

 test. The lobulated surface of the " float " chamber is faintly 



