70 



HISTORICAL PALEONTOLOGY. 





li^ife 1 "'' " ."^5 



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

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

 Giimbel, &c.) Stated briefly, the structure of Eosoon, as ex- 

 hibited by the microscope, is as follows: 



The concentrically-laminated mass of Eozo'dn is composed 

 of numerous calcareous layers, representing the original skele- 

 ton of the organism (fig. 23, b). These calcareous layers serve 

 to separate and de- 

 fine a series of cham- 

 bers arranged in sue- >- . '...,. ".....^^ 



cessive tiers, one 

 above the other (fig. 

 23, A, B , C) ; and 

 they are perforated 

 not only by passages 

 (fig. 23, c), which 

 serve to place suc- 

 cessive tiers of cham- 

 bers in communica- 

 tion, but also by a 

 system of delicate 



branching canals (fig. 



Fig. 23. Diagram of a portion of Eozoon cut verti- 



23, d), Moreover, cally. A, B, C, Three tiers of chambers communicating 



tViA ^ntral onrl r\rin with one another by slightly constructed apertures: a a, 



~ The true shell-wall, perforated by numerous delicate 



cipal portion of each tubes; & 6, The main calcareous skeleton ("intermedi- 

 ate skeleton"); c, Passage of communication ("stolon- 



calcareous layer, With passage") from one tier of chambers to another; d, 

 .1, '. A 1 Ramifying tubes in the calcareous skeleton. (After 



canal- Carp enter.) . 

 system just spoken 



of, is bound both above and below by a thin lamina which has 

 a structure of its own, and which may be regarded as the proper 

 shell-wall (fig. 23, a a}. This proper wall forms the actual lin- 

 ing of the chambers, as well as the outer surface of the whole 

 mass; and it is perforated with numerous fine vertical tubes 

 (fig. 24, a a), opening into the chambers and on to the sur- 

 face by corresponding fine pores. From the resemblance of 

 this tubulated layer to similar structures 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 parti- 

 tions, which are so far imperfect as to allow of a free communi- 

 cation between contiguous chambers. In the original condition 



