ORGANIC DEPENDENCE AND DISEASE 33 



thusiasm, for no service to this science, whether in fact 

 or philosophy, is more competent or more needed than 

 the evidence which lies here buried. To Walcott, who has 

 lifted the veil from the unsuspected specialization of the 

 Cambrian fauna and, with Barrande, has taught us to re- 

 gard that fauna, not as primitive but a venerable monument 

 of life, we owe our best knowledge of life in the still earlier 

 ages. 



Out of the vast Precambrian ages and its great seas 

 which, in view of the high specialization of the rich Cam- 

 brian fauna, must have laid down fossiliferous sediments 

 for inconceivable ages, we know immense growths of lime 

 deposits built up as reefs in the seas like the corals of today 

 and in whose formation algal life seems to have played 

 effective part. There has also been described a spongelike 

 skeleton called Atikokamnia (A. lawsoni and A. irregularis 

 Walcott) from the Steeprock series of Ontario, an organism 

 so primitive in its skeletal characters that its reference even 

 to the sponges lies in doubt. 1 



Walcott 2 has described as ' * Micrococcus sp. indet.," a 

 bacterium from the Algonkian (Precambrian) of Gallatin 

 county, Montana, which the bacteriologist Kligler 3 regards 

 as close to the existing Nitrosococcus which derives its ni- 

 trogen from ammonium salts. "The cell structure of the 

 Algonkian and of the recent Nitrosococcus bacteria is very 

 primitive and uniform in appearance, the protoplasm being 

 naked or unprotected. ' ' With this point before us we are 

 confronted by the impressive inference that this simplest 

 of organic structures has defied change and the ages. The 

 type at least has not failed to find its appropriate surround- 

 ings or to adjust itself readily to change in them. It is the 



1 It appears from the comments of Walcott that we must not yet regard the 

 horizon of this organism finally established, though Van Hise, Leith and the 

 discoverer, Lawson, regard it as from true sediments of the Precambrian Hu- 

 ronian. 



2 Proc. National Academy of Sciences, v. 1, p. 256, 1915. 



3 See Osborn's "Origin and Evolution of Life," 1917, p. 85. 



