182 THE DAWN OF LIFE. 



canaliculi not visible in this slice. Fig. 2_, from the 

 same specimen^ sliows the termination of one of the 

 canals against the proper wall^ its end expanding 

 into a wide disc of sarcode on the surface of the wall;, 

 as may be seen in similar structures in modern 

 Foraminifera. In this specimen the canals are beau- 

 tifully smooth and cylindrical^ but they sometimes 

 present a knotted or jointed appearance, especially in 

 specimens decalcified by acids, in which perhaps some 

 erosion has taken place. They are also occasionally 

 fringed with minute crystals, especially in those speci- 

 mens in which the calcite has been partially replaced 

 with other minerals. Fig. 3 shows an example of 

 faulting of the proper wall, an appearance not in- 

 frequently observed; and it also shows a vein of 

 chrysotile crossing the line of fault, and not itself 

 affected by it — a clear evidence of its posterior origin. 

 Figs. 4 and 5 are examples of specimens having 

 the canals filled with dolomite, and showing ex- 

 tremely fine canals in the interstices of the others : 

 an appearance observed only in the thicker parts of 

 the skeleton, and when these are very well preserved. 

 These dolomitized portions require some precautions 

 for their observation, either in slices or decalcified 

 specimens, but when properly managed they show 

 the structures in very great perfection. The speci- 

 men in fig. 5 is from an abnormally thick portion of 

 intermediate skeleton, having unusually thick canals, 

 and referred to in a previous chapter. 



One object which I have in view in thus minutely 



