Dr. W. B. Carpenter on Eozoon Canadense. 327 



shown on a former occasion *, has its peculiar advantages ; and the 

 combination of both, here permitted by the peculiar mode in which 

 the Eozoon has become fossilized, gives us a most complete repre- 

 sentation not only of the skeleton of the animal, but of its soft sarcode- 

 body and its minute pseudopodial extensions as they existed during 

 life. In well-preserved specimens of Eozoon, the shelly substance 

 often retains its characters so distinctly, that the details of its structure 

 can be even more satisfactorily made out than can those of most of the 

 comparatively modern Nummulites. And even the hue of the original 

 sarcode seems traceable in the canal-system ; so exactly does its aspect, 

 as shown in transparent sections, correspond with that of similar 

 canals in recent specimens of Polystomella, Calcarina, &c. in which 

 the sarcode-body has been dried. 



This last circumstance appears to me to afford a remarkable con- 

 firmation of the opinion formed by Mr. Sterry Hunt upon minera- 

 logical grounds — that the siliceous infiltration of the cavities of the 

 Eozoon was the result of changes occurring before the decomposition 

 of the animal. And the extraordinary completeness of this infil- 

 tration may be the result (as was suggested by Professor Milne- 

 Edwards with regard to the infiltration of fossil bones and teeth, in 

 the course of the discussion which took place last year on the Abbe- 

 ville jaw) of the superiority of the process of 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 cham- 

 bers of each tier for the most part communicating very freely with 

 each other (like the secondary chambers of Carpentericcf), so that 

 the segments of the sarcodic ^er which occupied them were inti- 

 mately 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 

 tubuli, so as exactly to correspond with that of Nummulites, Cyclo- 

 clypeus, and OperculinaX; and even these minute tubuli are so pene- 

 trated 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 homogeneous shell-substance ; and these layers represent the "in- 

 termediate" or "supplemental" skeleton which I have described in 

 several of the larger Foraminifera, and which attains a peculiar 

 development in Calcarina §. And, as in Calcarina and other recent 

 and fossil Foraminifera, this "intermediate skeleton" is traversed 

 by a " canal-system " || that gave passage to the prolongations of the 



* Memoir on Polystomella, in Phil. Trans, for 1860, pp. 538, 540. 



t Phil. Trans. 1860, p. 566. \ Ibid. 1856, p. 558, and pi. xxxi. figs. JJ& 10. 



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



