300 On the Structure and Position of Eozoon Canadense. 



than a Rhizopod of the Foraminiferal type ; its homogeneous 

 jelly-like substance not being even invested by the semblance 

 of a membrane, so that its pseudopodial extensions, when they 

 meet each other, coalesce like the glutinous threads separately 

 proceeding from the spinnerets of a Spider. But it is possible 

 to conceive of a system of rocks preceding the Laurentian, as 

 the Laurentian preceded the Cambrian, and the Cambrian pre- 

 ceded the Silurian ; and it would be a most rash assumption 

 to maintain that the first appearance of Eozoon above the Lau- 

 rentian horizon really marked the dawn of animal life on our 

 planet. As Dr. Dawson has justly remarked, "though the 

 abundance and wide distribution of Eozoon, and the important 

 part it seems to have acted in the accumulation of limestone, 

 indicate that it was one of the most prevalent forms of animal 

 existence in the seas of the Laurentian period, they do not 

 imply the non-existence of other beings. On the contrary, 

 independently of the indications afforded by the limestones 

 themselves, it is evident that in order to the existence and 

 growth of these large rhizopods, the water must have swarmed 

 with more minute animal and vegetable organisms on which 

 they could subsist." 



It would be difficult, I think, to find a more ' ' pregnant 

 instance " of the value of Microscopical investigation than that 

 which is afforded by the discovery of which I have now given 

 an account ; a discovery which I am strongly disposed to regard 

 as only the first of many similar results, which will follow its 

 intelligent application to the study of the internal structure of 

 other fossils, hitherto known only by their external forms. The 

 organic structure and precise zoological affinities of a body which 

 was at first supposed to be a product of purely physical opera- 

 tions, have been shown to be determinable with certainty from the 

 examination of a particle which a pin's head would cover ; and 

 we are thus enabled to predicate the nature of the living action 

 by which it was produced, at a Geological epoch whose remoteness 

 in time carries us even beyond the range of the imagination, with 

 no less certainty than the Astronomer can now, by the aid of 

 spectrum-analysis, determine the chemical and physical con- 

 stitution of bodies whose remoteness in space alike transcends 

 our power to conceive. 



EXPLANATION OP PLATES. 



The Coloured Plate represents the various appearances 

 exhibited by a specimen of Eozoon Canadense, which has been 

 macerated in dilute acid, so as to dissolve away the calcareous 

 shell which originally contained the body of the animal, now 

 replaced by its model in green serpentine. In the lower part 

 of the plate the segments are seen to be united into continuous 



