WHAT IS EOZOON ? 87 



glistening fringe ; and wlien this fringe is examined witb a 

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

 multitude of extremely delicate aciculi, standing side by side 

 like tlie fibres of asbestos. These, it is obvious, are the inter- 

 nal casts of the fine tubuli which perforated the proper wall of 

 the chambers, passing directly from its inner to its outer 

 surface ; and their presence in this situation affords the most 

 satisfactory confirmation 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 supplemental or intermediate skeleton such as presents 

 itself in all the more massive forms of the ISTummuline series; 

 but a deposit of this form of shell-substance, readily dis- 

 tinguishable by its homogeneousness from the finely tubular 

 shell immediately investing the segments of the sarcode-body, 

 is the source of the great thickening which the calcareous 

 zones often present in vertical sections of Eozoon. The pre- 

 sence of this intermediate skeleton has been correctly indi- 

 cated 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 

 intermediate skeleton, and is expressly designed to supply a 

 channel for its nutrition and augmentation. Of this canal 

 system, which presents most remarkable varieties in dimen- 

 sions 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. 



" It does not appear to me that the canal system takes its 

 origin directly from the cavity of the chambers. On the con- 

 trary, I believe that, as in Calcarina (which Dr. Dawson has 

 correctly referred to as presenting the nearest parallel to it 

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



