"The successive layers, each having its own proper wall, are often superposed one upon another without the intervention of any supplemental or intermediate skeleton such as presents itself in all the more massive forms of the Nummuline series; but a deposit of this form of shell-substance, readily distinguishable by its homogeneousness from the finely tubular shell immediately investing the segments of the sarcode-body, is the source of the great thickening which the calcareous zones often present in vertical sections of Eozoon. The presence of this intermediate skeleton has been correctly indicated by Dr. Dawson; but he does not seem to have clearly differentiated it from the proper wall of the chambers. All the tubuli which he has described belong to that canal system which, as I have shown,[T] is limited in its distribution to the intermediate skeleton, and is expressly designed to supply a channel for its nutrition and augmentation. Of this canal system, which presents most remarkable varieties in dimensions and distribution, we learn more from the casts presented by decalcified specimens, than from sections, which only exhibit such parts of it as their plane may happen to traverse. Illustrations from both sources, giving a more complete representation of it than Dr. Dawson's figures afford, have been prepared from the additional specimens placed in my hands. [Footnote T: _Op. cit._, pp. 50, 51.] "It does not appear to me that the canal system takes its origin directly from the cavity of the chambers. On the contrary, I believe that, as in Calcarina (which Dr. Dawson has correctly referred to as presenting the nearest parallel to it among recent Foraminifera), they originate in lacunar spaces on the outside of the proper walls of the chambers, into which the tubuli of those walls open externally; and that the extensions of the sarcode-body which occupied them were formed by the coalescence of the pseudopodia issuing from those tubuli.[U] [Footnote U: _Op. cit._, p. 221.]