EOZOOX 



841 



of which, as well as its sectional view, is shown in fig. 642. And 

 when this layer is examined with a sufficient 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 fre- 

 quently grouped in converging 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 

 IQQO O 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 which was in the Author's 



Cession) ; and their arrangement presents all the varieties which 

 j been mentioned as existing in the shells of Operculina. Thus 



FIG. 643. Vertical section of a portion of one of the calcareous lamellae of 

 Eozoon canadense : a a, Nummuline layer perforated by parallel tubuli, 

 which show a flexure along the line a' a' ; beneath this is seen the inter- 

 mediate skeleton, c, c, traversed by the large canals, b, b, and by oblique 

 cleavage planes, which extend also into the Nummuline layer. 



these delicate and beautiful silicious fibres represent those pseudo- 

 podial 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. 



In the upper part of the ' decalcified ' specimen shown in fig. 642 

 it is to be observed that the segments are confusedly heaped together 

 instead of being regularly arranged in layers, the lamellated mode 

 of growth having given place to the acervuline. This change is by 

 no means uncommon among Foraminifera, an irregular piling 

 together of the chambers being frequently met with in the later 

 growth of types whose earlier increase takes place upon some much 



