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Fig. 43. — Diagram of a portion of Eozoon cut verti- 

 cally. A, B, c, Three tiers of chambers communicating 

 with one another by slightly constricted apertures ; a a, 

 The true shell-wall, perforated by numerous delicate 

 tubes ; b b, The main calcareous skeleton (" intermedi- 

 ate skeleton ") ; c, Passage of communication (" stolon- 

 passage ") from one tier of chambers to another ; d, 

 Ramifying tubes in the calcareous skeleton. (After 

 Carpenter.) 



crystallised or otherwise altered by the metamorphic agencies which 

 have affected the entire mass of the enclosing rock ; and the original 

 chambers between successive layers of the shell have been filled up 

 with serpentine or some other silicate, which has taken the place of 

 the living matter which, to 



begin with, is supposed to r— ^— — — — . - ; _ —■. 



have occupied these spaces. i J....,, ,„..„,' ,..■«.„...<««**««, (,'.■ 



The serpentinous infilling has r "" " , "' 



been deposited from solution 

 in water, and has not only 

 usually occupied the large 

 chambers between the cal- 

 careous laminae, but has also 

 more or less extensively pen- 

 etrated into the larger canals 

 or even the minuter tubuli 

 which traverse the substance 

 of these laminae. Placing 

 this interpretation upon the 

 observed structure of -Eozoon, 

 the central and principal por- 

 tion of each calcareous lam- 

 ina (fig. 43, b b) is regarded 

 as corresponding with the 

 " supplemental skeleton " of 

 such a Foraminifer as Cal- 

 carina or Nunwiulina, while 

 the branching tubes which 



traverse the lamina (fig. 43, d), are considered to represent the " canal- 

 system " of the same. Moreover, the narrow, transversely striated band 

 or selvage, which normally bounds each calcareous lamina above and 

 below (fig. 43, a a), is regarded as corresponding with the "proper wall" 

 of such a Foraminifer as Nummuli?ia, and has therefore been com- 

 monly spoken of as the " Nummuline layer." On this view, therefore, 

 the so-called "proper wall" is part of the actual skeleton, and the 

 vertical lines which traverse it represent minute tubules, which open 

 into the chambers and on the surface by correspondingly fine pores. 

 It need only be added that if the above explanation of the observed 

 structure of Eozoon be accepted, it then takes its place in the series 

 of the Foraminifera as a gigantic and aberrant member of the Num- 

 mulinidce, having a quite special interest and importance as both the 

 oldest known fossil and also the largest of known Protozoans. 



On the other hand, very weighty objections have been urged against 

 the theory of the organic nature of Eozoon by many observers, and more 

 especially by Mobius in Germany and King and Rowney in Britain. 



It would be out of place here to attempt to discuss these objections, but 

 the following are, in brief, the more important arguments which have 

 been brought forward against the organic nature of Eozobfi and in favour 

 of the view that it is a purely mineral structure : — 



a. The structure to which the name of Eozoon is applied is found in 

 highly crystalline rocks, and in parts of these which are much broken 

 and altered. Moreover, no unquestionable organic remains have been 

 discovered in association with Eozoon. 



b. The general form of Eozoon is very irregular, and though its minute 

 structure (supposing it to be organic) would show that it belongs to the 



