1864.] 



and Affinities of Eozoon Canadense. 



547 



substitution, in which the animal matter is replaced (particle by particle) 

 by some mineral substance, over that of mere penetration. 



The Eozoon in its living state might be likened to an extensive range of 

 building made up of successive tiers of chambers, the chambers of each tier 

 for the most part communicating very freely with each other (like the 

 secondary chambers of Carpenteria*, so that the segments of the sarcodic 

 layer which occupied them were intimately connected, as is shown by 

 the continuity of their siliceous models. The proper walls of these 

 chambers are everywhere formed of a pellucid vitreous shell-substance 

 minutely perforated with parallel tubuh, so as exactly to correspond with 

 that of Nmnmulites, Cycloclypeus, and Operculinaf; and even these minute 

 tubuli are so penetrated by siliceous infiltration, that when the calcareous 

 shell has been removed by acid, the internal casts of their cavities remain 

 in the form of most delicate needles, standing parallel to one another on 

 the solid mould of the cavity of the chamber, over which they form a 

 delicate filmy layer. 



But, between the proper walls of the successive tiers of chambers, there 

 usually intervene layers of very variable thickness, composed of a homo- 

 geneous shell-substance ; and these layers represent the intermediate " or 

 "supplemental" skeleton which I have described in several of the larger 

 FoRAMiNiFERA, and which attains a peculiar development in GalcarinaX' 

 And, as in Calcavina and other recent and fossil Foraminifera, this "in- 

 termediate skeleton" is traversed by a " canal-system " § that gave passage 

 to the prolongations of the sarcode-bod}^, by the agency of which the calca- 

 reous substance of this intermediate skeleton seems to have been deposited. 

 The distribution of this canal-system, although often well displayed in 

 transparent sections, is most beautifully shown (as in Polystomella ||) by 

 the siliceous casts which are left after the solution of the shell, these casts 

 being the exact models of the extensions of the sarcode-body that origi- 

 nally occupied its passages. 



In those portions of the organism in which the chambers, instead of 

 being regularly arranged in floors, are piled together in an " acervuline " 

 manner, there is little trace either of "intermediate skeleton" or of 

 "canal-system"; but the characteristic structure of their proper walls is 

 still unmistakeably exhibited. 



Whilst, therefore, I most fully accord with Dr. Dawson in referring the 

 Eozoon Canadense, notwithstanding its massive dimensions and its zoophytic 

 mode of growth, to the group of Foraminifera, I am led to regard its 

 immediate affinity as being rather with the Nummuline than with the 

 Rotaline series — that affinity being marked by the structure of the proper 

 wall of the chambers, which, as I have elsewhere endeavoured to show 



* Phil. Trans. 1860, p. 5G6. f Ibid. 1856, p. 558, and pi. xxxi. figs. 9 & 10. 



X Ibid. 1860, p. 553. § Ibid. I860, p. 554, plate xx. fig. 3. 



II Ibid. 1860, plate xviii. fig. 12. 



^ Introduction to the Study of the Foraminifera, chap. iii. 



