268 ]M. Otto Halm on Eozoon canadeiise. 



For in its indeterminate zoophytic mode of growth it agrees 

 with Polytre'nia ; in the incomplete separation of its chambers 

 it has its parallel in Cmyenteria ; whilst in the high develop- 

 ment of its intermediate skeleton and of the canal-system by 

 which this is nom-ished, it finds its nearest representative in 

 Calcarina. Its calcareous layers were so superposed one upon 

 another, as to include between them a succession of '■ storeys ' 

 of chamhers ; the chambers of each ' storey ' usually opening 

 one into another like apartments en siiite] but being occasionally 

 divided by complete septa. These sejjta are traversed by 

 passages of communication between the chambers which they 

 separate, resembling those which, in existing types, are occu- 

 pied by stolons connecting together the segments of the sarcode- 

 body. Each layer of shell consists of two finely tubulated or 

 ' Nummuline ' lamellas, which form the boundaries of the 

 chambers beneath and above, serving (so to speak) as the ceiling 

 of the former, and as the floor of the latter ; and of an inter- 

 vening deposit of homogeneous shell-substance, which consti- 

 tutes the ' intermediate skeleton.' The thickness of this 

 interposed layer varies considerably in different parts of the 

 same mass, being in general greatest near its base, and pro- 

 gressively diminishing towards its upper surface. The 'inter- 

 mediate skeleton ' is occasionally traversed by large passages, 

 which seem to establish a connection between the successive 

 layers of chambers; and it is penetrated by arborescent systems 

 of canals, which are often distributed both so extensively and 

 so minutely through its substance, as to leave very little of it 

 without a branch. 



'' § 398. Now in the fossilized condition in which Eozoon is 

 most commonly found, not only the cavities of the chambers, 

 but the canal-systems to their smallest ramifications, are filled 

 up by the siliceous infiltration which has taken the place of 

 the original sarcode-body ; and thus, when a piece of this 

 fossil is subject to the action of dilute acid, by which its 

 calcareous portion is dissolved away, we obtain an internal 

 cast of its chambers and the canal-system, which, though 

 altogether dissimilar in arrangement^ is essentially analogous 

 in character to the ' internal casts' represented in figs. 258, 259. 

 This cast presents us, therefore, with a model in hard serpen- 

 tine of the soft sarcode-body which originally occupied the 

 chambers, and extended itself into the ramifying canals of 

 the calcareous shell ; and, like that of Polystomella, it affords 

 an even more satisfactory elucidation of the relations of these 

 parts, than we could have gained from the study of the 

 living organism. We see that each of the layers of serpen- 

 tine forming the lower part of such a specimen is made 



