422 Mr. H. J. Carter on the Relation of the Canal-System 



while the canal-system is entirely outside the tubuli and the 

 chamber with which they are connected. Thus the flat sur- 

 face of the vertically compressed chamber on either side of 

 the Operculina, as its ammonite-like form lies horizontally on 

 the table, is vertically pierced by the tubuli ; while the narrow 

 part or vertical sides of the compressed chamber, which is con- 

 cealed within the test, is pierced alone by the ramuli coming 

 off from the large branches of the canal-system which border 

 upon the chamber all round. 



Secondly, that as the single plane of chambers of Operculina 

 is multiplied vertically in the Nummulite, the same structure, 

 mutatis mutandis, is here repeated, while the tubuli go from 

 chamber to chamber ; and nothing interferes with this arrange- 

 ment in the whole pile of chambers until the tubuli thus, at 

 last, open on the surface. 



The reason of this is obvious ; for the tubuli transmit the 

 sarcode from the chamber, which appears to be successively 

 engaged in forming the layers of the test, while there are no 

 tubuli in the contracted sides of the chamber, which, being 

 covered by the surface-layer of the test, do not need them, 

 but instead are pierced by the ramuli of the canal-system, 

 which thus communicate with the interior of the chamber. 



The function of the canal-system has not yet been discovered ; 

 but the main canals, which border the contracted sides of the 

 chamber (viz. that part of it within the test) all round, send off 

 three sets of branches, viz. : — 1st, those which penetrate the 

 "contracted sides" of the chamber ; 2nd, those which open on 

 the surface of the smooth areae of the test surrounding the 

 chamber ; and, 3rd, those which open on the convex surface 

 of the marginal cord. The latter I have been able to show 

 distinctly in a preparation lately made of a portion of the mar- 

 ginal cord of Nummulites laivigatus, where, as in Operculina, 

 their apertures appear like puncta scattered over the convex 

 surface of the cord along the lines of the amorphous matter 

 which fills up the interstices between the hard crystalline, fusi- 

 form, spicule-like bodies that not only form the surface of the 

 cord here, as in Operculina, but, in some specimens of Oper- 

 culina, are continued inwards over the intercameral spaces to 

 the preceding turn of the spire, showing that Dr. Carpenter 

 is quite wrong when he states that this structure " is due to 

 the peculiar manner in which the homogeneous substance of 

 which it [the marginal cord] is composed is traversed by the 

 ' marginal plexus' " (' Introduction to Study of Foraminifera,' 

 p. 257, 1862) — since there is no "plexus " here, any more than 

 in the marginal cord in direct contact with the spicular struc- 

 ture, simply because the latter is on the surface of the test, 



