172 Mr. H.J. Carter on the Form and Structure 



kind may exist at the termination of the spicular cord, for this 

 purpose ; but, then, it has nothing to do with the spicular cord 

 itself, of the natural termination and uses of which I am equally 

 ignorant. It should here also be mentioned, that when a 

 thoroughly empty shell, which may be known by its pearly 

 whiteness, is gently laid on the surface of a solution of carmine, 

 so as to float there, the latter is seen, first to colour the margin, 

 then the interseptal vessels become filled, and lastly the walls of 

 the chambers; none of the semitransparent parts of the shell 

 become coloured. This will take place sometimes in a few hours, 

 but with some shells it requires a day or two for its completion. 

 By keeping one side of the shell dry the air is enabled to pass 

 out of it, while the solution enters the depending side, and in 

 this way the whole of the hollow structure of the shell becomes 

 coloured. When the shell is washed and dried in this state, the 

 carmine is seen to be chiefly in the interseptal vessels, and this 

 is perhaps the best way of tracing out the terminations, or rather 

 origins, of the ramusculi. On the other hand, when the shell is 

 placed in pure water and watched with a magnifying glass, a 

 stream of carmine particles will be seen slowly issuing from the 

 vessels of the marginal plexus, at the broken end of the spicular 

 cord, or from any other part of the large whorls, where an inter- 

 septal vessel may have been broken ; and after a time, according 

 with that which the shell has taken to imbibe the colouring 

 matter, it will become perfectly white again. Whether this be 

 owing to the watery distension of the gummy fluid suspending 

 the carmine, or a natural consequence of the structure of the 

 shell itself, further observation must determine. The fact of the 

 carmine accumulating at the orifices of the ramusculi, as it would 

 in a filter, seems also, with what has just been stated, to point 

 out the course of circulation in them ; and if we may be allowed 

 to carry out the analogy still further, which is now seen to exist 

 so strikingly between Foraminifera and Porifera, we might 

 compare the interseptal circulation in the former to the aqueous 

 circulation in the latter, and thence might infer, that the water 

 entered by the ramusculi or small pores, and came out by the 

 larger ones, gathered together into one vessel, opening in its 

 natural state at the end of the spicular cord ; but, until a perfect 

 specimen be obtained to determine this, all must of course re- 

 main conjectural. 



Growth. — From what I have stated respecting the existence 

 of a substance, resembling the cuticle of shells, over the external 

 surface of Operculina Arabica, and the presence of innumerable 

 puncta, which appear to be connected by tubular communica- 

 tions with the chambers beneath, it is not unreasonable to infer, 

 that by this arrangement successive additions may be made to 



