140 



PROTOZOA. 



tubulated structure. In parts in which this structure is preserved, the 

 crystalline calcite of the calcareous laminae is seen to be traversed by 

 branching and dendritic canals (fig. 41, B and c). Some of these canals 

 (fig. 41, b) are of comparatively large size, and these are generally more 

 or less extensively occupied with an infilling of serpentine, though some- 

 times partially filled with calcite. In connection with these large canals 

 are much more delicate canaliculi or tubules (fig. 41, C and d), which run 

 more or less parallel with one another, or have a tufted arrangement, and 

 which are commonly filled with transparent calcite. At the edges of the 

 calcareous laminae these delicate and branching tubules often appear to 

 terminate in a narrow belt or selvage (the so-called "proper wall" or 

 " Nummuline layer" of Carpenter and Dawson), which has a transversely 

 striated aspect, as if composed of parallel fibres or traversed by innumer- 





lillSife^ 



Fig. 42. — Portion of one of the cakareous layers of Eozoon, magnified ioo diameters, a a, 

 The proper wall (" Nummuline layer ") of one of the chambers, showing the fine vertical tubuli 

 with which it is penetrated, and which are slightly bent along the line a a ; c c, The inter- 

 mediate skeleton, with numerous branched canals. The oblique lines are the cleavage-planes 

 of the carbonate of lime, extending across both the intermediate skeleton and the proper wall. 

 (After Carpenter.) 



able minute tubuli (fig. 41, D, w). According to the observations of 

 Dawson, this narrow selvage, or " proper wall," consists of " finely divided 

 tubes, similar to those of the canal-system, and composed of its finer sub- 

 divisions placed close together so as to become approximately parallel " 

 (fig. 42). 



The actual structure of Eozoon being as above briefly described, we 

 may in the next place shortly consider the interpretation placed upon this 

 structure by those who regard it as organic in origin, and who, like \V. B. 

 Carpenter, Dawson, and Rupert Jones, consider it to represent an ancient 

 type of the Foraminifera. Upon this view — which a reference to the 

 subjoined diagrammatic figure (fig. 43) will render readily intelligible — 

 the calcareous laminae (b b) of a mass of Eozoon represent the original 

 calcareous skeleton of a gigantic Foraminifer, while the serpentinous 

 layers represent the successive tiers of chambers separating successive 

 laminae of the skeleton. The calcareous skeleton itself has been largely 



