124 



PROTOZOA. 



may be regarded as the proper shell- wall (fig. 26, a a). This 

 proper wall forms the actual lining of the chambers, as well 

 as the outer surface of the whole mass ; and it is perforated 

 with numerous fine vertical tubes (fig. 27, a a\ opening into 

 the chambers and on the surface by corresponding fine pores. 

 From the resemblance of this tubulated layer to similar struc- 

 tures in the shell of the Nummulite, it is often spoken of 

 as the " Nummuline layer." The chambers are sometimes 

 piled up one above the other in an irregular manner ; but 

 they are more commonly arranged in regular tiers, the 

 separate chambers being marked off from one another by 

 projections of the wall in the form of partitions, which are 

 so far imperfect as to allow of a free communication between 

 contiguous chambers. In the original condition of the 

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



Fig. 27. 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 intermediate skeleton and the 

 proper walL (After Carpenter.) 



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 also penetrated the minute tubes of the proper wall 

 and the branching canals of the intermediate skeleton. In 



