28 DE. CAEPENTEE'S EESEAECHES ON THE FOEAMENTFEEA. 



the interseptal passages branch off from these two spiral canals, is well seen in fig. 1, 

 Plate VI., and also in fig. 10, Plate IV.; and this arrangement is shown in fig. 5, 

 Plate IV. to extend to the septa between the chambers of the innermost convolution. 

 The relations of the different parts of the system are brought extremely well into view 

 in fig. 12, Plate IV., which represents a tangential section of a young shell, the rapid 

 curve of whose spire causes the planes of even the contiguous septa to vary greatly in 

 their direction. The spiral canals, though only running along the angles of the mar- 

 ginal cord, pretty obviously communicate with the plexus of passages which it contains ; 

 and thus the interseptal system of one whorl is brought into direct connexion with that 

 of the preceding. It is to be remembered, however, that independently of such con- 

 nexion, the spiral mode of growth of itself brings about a continuity of the canal-system 

 throughout, by means of the marginal plexus ; the consecutive whorls not being added 

 one to another like the successive annuli of Cycloclypeus, each of which is (so to 

 speak) closed or complete in itself; but being formed by the prolongation of the spiral 

 lamina and of the marginal cord, which may be considered as always open to indefinite 

 extension. 



160. In regard to the uses of this canal-system, I have not at present anything to add 

 to what I have already stated when describing its distribution in Cycloclypeus (^f 107) : 

 I shall have the opportunity, however, of discussing them more fully in a subsequent 

 Memoir upon forms in which this system is still more remarkably developed. 



161. I have attempted to determine by a re-examination of my preparations of Num- 

 mulites, with the additional light afforded by the structure of Operculina, whether an 

 arrangement of the canal-system prevails in the former at all comparable to that which 

 I have shown to exist in the latter. In those which have undergone the ordinary 

 fossilizing process, it is difficult to discover more than vague indications of its existence. 

 But the peculiar process of silicification of Foraminifera, to which attention has been 

 recently drawn by Professor EHRENBERG *, has afforded an unexpected verification of the 

 anticipations which the similarity of these two genera in other points of structure had 

 led me to form as to this. For by the infiltration of silex tinged with silicate of iron 

 into the cavities of Foraminifera, whilst their calcareous shells have undergone decom- 

 position and removal, a most perfect series of casts are presented, not merely of the 

 chambers, but of the canal-system where this exists. And in his figure of such a cast 

 of Nummulites striata (taf. 5. fig. 2), Professor EHRENBERG has given a most beautiful 

 representation of the canal-system of the marginal cord, and of its communications with 

 the interseptal canals, so closely corresponding with that which, long before the publica- 

 tion of his memoir, I had worked out in Operculina^ that no doubt can fairly remain 

 as to the essential similarity between these two types in this important feature of their 

 organization }*. 



* Uber den G-riinsand und seine Erlauterung des organiachen Lebens. Aus den Abhaldlungen der 

 Konigl. Akademie der Wissenschaften zu Berlin, 1855. 



t I may here remark upon the confirmation afforded by other parts of this most valuable memoir to the 

 results of my researches upon Orbitolites and Cycloclypeits ; the various figures given by Professor EHBENBEEG 



