STEUCTUEE OF EOZOON CANADENSE. 5 L9 



presented in Figs. 258, 259. This Cast presents us, therefore, 

 with a model in hard Serpentine of the soft Sarcode-body which 

 originally occupied the Chambers, and extended itself into the 

 ramifying Canals, of the Calcareous Shell ; and, like that of 

 Polystomella (§ 390), it affords an even more satisfactory eluci- 

 dation of the relations of these parts, than we could have gained 

 from the study of the living Organism. We see that each of the 

 layers of Serpentine, forming the lower part of such a specimen, is 

 made up of a number of coherent Segments, which have only 

 uudergone a partial separation ; these appear to have extended 

 themselves horizontally without any definite limit ; but have here 

 and there developed new segments in a vertical direction, so as to 

 give origin to new layers. In the spaces between these successive 

 layers, which were originally occupied by Calcareous Shell, we see 

 the ' internal casts ' of the branching Canal-System ; which give 

 us the exact models of the extensions of the Sarcode-body that 

 originally passed into them. — But this is not all. In specimens 

 in which the Nummuline Layer constituting the 'proper wall' of 

 the chambers was originally well preserved, and in which the 

 Decalcifying process has been carefully managed (so as not, by too 

 rapid, an evolution of Carbonic acid gas, to disturb the arrange- 

 ment of the Serpentinous residuum), that layer is represented by 

 a thin white film covering the exposed surfaces of the segments ; 

 the superficial aspect of which, as well as its sectional view, are 

 shown in Fig. 2. And when this layer is examined with a suffi- 

 cient magnifying power, it is found to consist of extremely minute 

 needle-like fibres of Serpentine, which sometimes stand upright, 

 parallel, and almost in contact with each other, like the fibres of 

 Asbestos (so that the film which they form has been termed the 

 ' Asbestiform layer'), but which are frequently grouped in con- 

 verging brush-like bundles, so as to be very close to each other in 

 certain spots at the surface of the film, whilst widely separated in 

 others. Now these fibres, which are less than 1 -10, 000 th of an 

 inch in diameter, are the 'internal casts' of the tubuli of the 

 Nummuline layer (a precise parallel to them being presented in 

 the 'internal cast' of a recent Amphistegina in the Author's 

 possession) ; and their arrangement presents all the varieties 

 which have been described (§ 391) as existing in the Shells of 

 Operculina. — Thus these delicate and beautiful Siliceous fibres 

 represent those pseudopodial threads of Sarcode, which originally 

 traversed the minutely-tubular walls of the chambers; and a 

 precise model of the most ancient Animal of which we have any 

 knowledge, notwithstanding the extreme softness and tenuity of 

 its substance, is thus presented to us with a completeness that is 

 scarcely even approached in any later Fossil. 



399. In the upper part of the ' decalcified ' specimen shown in 

 Fig. 2, it is to be observed that the segments are confusedly 

 heaped together, instead of being regularly arranged in layers, 



