116 THE CANADIAN NATURALIST. [April 



in recent examples of the Nurninuline type, is here far better dis- 

 played than it is in the majority of fossil Nunmiulites, in which the 

 tubuli have been filled up by the infiltration of calcareous matter, 

 rendering the shell-substance nearly homogeneous. In Eozoon these 

 tubuli have been filled up by the infiltration of a mineral different 

 from that of which the shell is composed, and therefore not coalesc- 

 ing with it ; and the tubular structure is consequently much more 

 satisfactorily distinguishable.. In decalcified specimens, the free mar- 

 gins of the casts of the chambers are often seen to be bordered with 

 a delicate white glistening fringe ; and when this fringe is examined 

 with a sufficient magnifying power, it is seen to be made up of a 

 multitude of extremely delicate aciculi, standing side by side like 

 the fibres of asbestos. These, it is obvious, are the internal casts 

 of the fine tubuli which perforated the proper wall of the cham- 

 bers, passing directly from its inner to its outer surface ; and their 

 presence in this situation affords the most satisfactory confirma- 

 tion of the evidence of that tubulation afforded by thin sections of 

 the shell-wall. 



The successive layers, each having its own proper wall, are often 

 superposed one upon another without the intervention of any sup- 

 plemental or intermediate skeleton such as presents itself in all the 

 more massive forms of the Nummuline series ; but a deposit of this 

 form of shell-substance, readily distinguishable by its homogeneous- 

 ness from the finely tubular shell immediately investing the seg- 

 ments of the sarcode-body, is the source of the great thickening 

 which the calcareous zones often present in vertical sections of 

 Eozoon. The presence of this intermediate skeleton has been 

 correctly indicated by Dr. Dawson ; but he does not seem to have 

 clearly differentiated it from the proper wall of the chambers. All 

 the tubuli which he has described belong to that canal-system 

 which, as I have shown, * is limited in its distribution to the in- 

 termediate skeleton, and is expressly destined to supply a channel 

 for its nutrition and augmentation. Of this canal-system, which 

 presents most remarkable varieties in dimensions and distribution^ 

 we learn more from the casts presented by decalcified specimens 

 than from sections, which only exhibit such parts of it as their plane 

 may happen to traverse. Illustrations from both sources, giving 

 a more complete representation of it than Dr. Dawson's figures 

 afford, have been prepared from the additional specimens placed in 

 my hands (plate, figure 7). 



* Op. cit., pp. 50, 51. 



