546 Dr. W. B. Carpenter on the Structure [Dec. 15, 



siliceous layers, these being most distinct in the basal portion. The speci- 

 mens which the kindness of Sir "William E. Logan has given me the oppor- 

 tunity of examining, are composed of carbonate of lime alternating with 

 serpentine — the calcareous layers being formed by the original skeleton of 

 the animal, whilst the serpentine has filled up the cavities once occupied 

 by its sarcode-body. In other specimens the carbonate of lime is replaced 

 by dolomite, and the serpentine by pyroxene, Loganite, or some other 

 mineral of which silex is a principal constituent. The regular alternation 

 of calcareous and siliceous layers which is characteristic of the basal por- 

 tion of these masses, frequently gives place in the more superficial parts to 

 a mutual interpenetration of these minerals, the green spots of the serpen- 

 tine being scattered over the surface of the section, instead of being col- 

 lected in continuous bands, so as to give it a granular instead of a striated 

 aspect. This difference we shall find to depend upon a departure from the 

 typical plan of growth, which often occurs (as in other Foraminifera) in the 

 later stages — the minute chambers being no longer arranged in continuous 

 tiers, but being piled together irregularly, in a manner resem.bling that in 

 which the cancelli are disposed at the extremities of a long bone. 



The minute structure of this organism may be determined by the micro- 

 scopic examination either of thin transparent sections, or of portions which 

 have been submitted to the action of dilute acid, so as to remove the cal- 

 careous shell, leaving only the siliceous casts of the chambers and other 

 cavities originally occupied by the substance of the animal. Each of these 

 modes of examination, as I have 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 

 representation 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 JEozoon, 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 FolystomeUa^ 

 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 mineralogical 

 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 infiltration may be the result 

 (as was suggested by Professor Milne-Edwards with regard to the infiltra- 

 tion of fossil bones and teeth, in the course of the discussion which took 

 place last year on the Abbeville jaw) of the superiority of the process of 



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



