On the Structure and Position ofEozoon Canadense. 295 



of sarcodic segments, it is obvious that where this surface has 

 been overgrown by a thick exogenous deposit of non-tubular 

 shell-substance, some more special provision must exist for 

 the origination of a new tier of chambers above this. Such a 

 provision seems to have been occasionally made by the exten- 

 sion of riband-like prolongations of sarcode, through large 

 passages left in the intermediate skeleton, proceeding from 

 the chambers beneath, and opening on its upper surface j for I 

 have not only occasionally met with such flattened passages in 

 transparent sections of the shell (Uncoloured Plate, Fig. 1, d), 

 but have still more frequently found the void spaces in decal- 

 cified specimens, left by the removal of the thickest layers of 

 the intermediate skeleton, to be traversed by the internal 

 casts of such passages, which seem to represent the sarcodic 

 stolons of the living animal body.* 



The origination of new layers, however, seems more fre- 

 quently to have taken place in a much larger extension of the 

 sarcode-body of the pre -formed layer; which either folded back 

 its margin over the surface already consolidated (in a manner 

 somewhat like that in which the mantle of a Oyprcea doubles 

 back to deposit the final surface-layer of its shell), or sent 

 upwards wall-like plates, sometimes of very limited extent, 

 but not unfrequently of considerable horizontal length, which, 

 after traversing the substance of the shell, spread themselves 

 out over its free surface. For it is frequently to be observed 

 in decalcified specimens, that two bands of serpentine (or other 

 infiltrating mineral), which represent two layers of the original 

 sarcode-body of the animal, approximate each other in some 

 part of their course, and come into complete continuity 

 (as on the left-hand side of the Coloured Plate), so that 

 the upper layer would here seem to have originated in a 

 folding-over of the lower. And even where these bands 

 are most widely separated, we find that they are commonly 

 held together by vertical dykes of the same material, which 

 traverse the intervening calcareous layers like trap-dykes 

 passing through a bed of sandstone. That such have not 

 been formed by mineral infiltration into accidental fissures in 

 the shell, but represent extensions of the sarcode-body of the 

 living animal, is indicated not merely by their distinct con- 

 tinuity with the horizontal layers, but also by the fact that 

 portions of the canal-system may frequently be traced into 

 connexion with them. 



The only information which seems to me yet wanting to 

 bring up our knowledge of the life-history of this organism to 

 the highest level of that (still far from complete, especially as 



* See the white bands passing from the middle of the lowest layer in the 

 Coloured Plate to the layer next above it. 



