THE LAURENTIAN AND HURONIAN PERIODS. 71 



of the organism, all these chambers, of course, must have 

 been filled with living matter; but they are found in the present 

 state of the fossil to be generally filled with some silicate, such 

 as serpentine, which not only fills the actual chambers, but has 



Fig. 24. Portion of one of the calcareous layers of Eozoon. magnified 100 diameters. 

 a a, The proper wall ("Nummuline layer") of one of the chambers, showing the fine 

 vertical tubuli with which it is penetrated, and which are slightly bent along the line 

 a' a', c c. .The intermediate skeleton, with numerous branched canals. The oblique 

 lines are the cleavage planes of the carbonate of lime, extending across both the in- 

 termediate skeleton and the proper wall. (After Carpenter.) 



also penetrated the minute tubes of the proper wall and the 

 branching canals of the intermediate skeleton. In some cases 

 the chambers are simply filled with crystalline carbonate of 

 lime. When the originally porous fossil has been permeated 

 by a silicate, it is possible to dissolve away the whole of the 

 calcareous skeleton by means of acids, leaving an accurate and 

 beautiful cast of the chambers and the tubes connected with 

 them in the insoluble silicate. 



The above are the actual appearances presented by Eozoon 

 when examined microscopically, and it remains to see how 

 far they enable us to decide upon its true position in the 

 animal kingdom. Those who wish to study this interesting 

 subject in detail must consult the admirable memoirs by Dr. 

 W. B. Carpenter and Principal Dawson : it will be enough 

 here to indicate the results which have been arrived at. The 

 only animals at the present day which possess a continuous 

 calcareous skeleton, perforated by pores and penetrated by 

 canals, are certain organisms belonging to the group of the 



