FORAMINIFERA. 



123 



are composed alternately of lighter and darker coloured lime- 

 stone. 



When first discovered, the masses of HJozodf\weYQ supposed 

 to be of a mineral nature ; but their striking general resem- 

 blance to the undoubted fossils which will be subsequently 

 spoken of under the name of Stromatopora was recognised by 

 Sir William Logan, and specimens were submitted for minute 

 examination, first to Principal Dawson, and subsequently to 

 Dr W. B. Carpenter. After a careful microscopic examina- 

 tion, these two distinguished observers came to the conclusion 

 that Eozoon was truly organic, and in this opinion they were 

 afterwards corroborated by other high authorities (Mr W. K. 

 Parker, Professor Eupert Jones, Mr H. B. Brady, Professor 

 Giimbel, &c.) Stated briefly, the structure of Eozoon, as 

 exhibited by the microscope, is as follows : 



The concentrically-laminated mass of Eozoon, as described 

 by Dr Carpenter and Principal Dawson, is composed of 

 numerous calcareous layers, representing the original skele- 

 ton of the organism 

 (fig. 26, V). These 

 calcareous layers serve 

 to separate and define 

 a series of chambers 

 arranged in successive 

 tiers, one above the 

 other (fig. 26, A, B, 

 c) ; and they are per- 

 forated not only by pas- 

 sages (fig. 26, c), which 

 serve to place succes- 

 sive tiers of chambers 

 in communication, but 

 also by a system of del- 

 icate branching canals 

 (fig. 26,rf). Moreover, 

 the central and princi- 

 pal portion of each calcareous layer, with the ramified canal- 

 system just spoken of, is bounded both above and below by 

 a thin lamina which has a structure of its own, and which 



Fig. 26. 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.) 



