D.— ZOOLOGY. 61 



of the premisses, 11 the argument does not seem without philosophic 

 interest : — that if the 7-foot graphite bed in Finland be of organic origin, 

 there may be a class or classes of terrestrial animals or plants which have 

 breathed air two or three times as long as those which left the sea in the 

 Devonian. 



The Laurentian coal, if coal it be, must mark the climax of a long 

 evolution in the seas of the still earlier Pre-Laurentian, and in that part 

 of our history must come the primary advance which Church has rightly 

 taught us to regard as the greatest step in evolution, the evolution of the 

 flagellates. Church claims that, since protoplasm appeared, we may 

 fairly estimate half the time elapsed as being required for the evolution of 

 the flagellate. 1 ' 2 If Dr. Church measures his time in years, the geological 

 record seems difficult to fit ; for the chaetopods, molluscs, Crustacea and 

 echinoderms of the Cambrian are clearly very old phyla. But the single 

 step in evolution is not a year but a generation, and there may well have 

 been as many generations of our ancestors before they became flagellates 

 as there have been since we have been multicellular. If we have 

 been ' higher animals,' averaging ten generations a year, for 1000 million 

 years, then some 10,000 million generations may have brought us from 

 jelly-fish to men. But 1000 generations a year would be a very moderate 

 number for flagellates and pre-flagellates, 13 so that 10 or 20 million years 

 would give them as many steps in evolution, to make a flagellate from 

 nothing, as it has taken us to build up a flagellate into that highest of all 

 living creatures, a member of the British Association (Section D). 



We are still lacking a satisfactory account of the early ocean in which 

 those fateful 20 million or 200 million years were passed, and in which life 

 began. I must relegate to a printed Appendix some arithmetical criticism 

 which I have ventured to make on Professor Joly's theory of the sea. 

 Resulting from that arithmetical discussion, I suggest as a working 

 hypothesis for biologists that, since the Pre-Cambrian, there have been no 

 variations in the mean salinity of the ocean so great as the difference 

 between the salinity in the Mediterranean and in the North Sea. 



The first ocean was more or less saline : it was also soaked with carbon- 

 dioxide. In the air there was no oxygen, but nitrogen, much water- 

 vapour, and carbon-dioxide in large quantities. Life is the history of 

 high carbon compounds, in which every atom of carbon has been in a 

 molecule of carbonic-acid gas. Volcanoes and springs have always been 



u Prof. A. C. Pickering (Geol. Mag. lxi, 1924, p. 31) supposes the moon to have 

 left the earth 700 million years ago. If we shorten this to 600 million it would account 

 for the cataclysm, and from the ratio given by Jeffreys (I.e. p. 229) it would be 30 million 

 years before the tides dropped to double their present height. But I am informed 

 that the mathematical theory of the earth's period of oscillation makes a geological 

 date for the moon's birth highly improbable. It seems from the maps conceivable 

 that in Torridonian times the tide might have swept right round the Northern 

 Hemisphere. 



12 A. H. Church, 1919 : ' The building of an autotrophic Flagellate,' p. 4 (citing 

 Naegeli and Minchin). Oxford University Press. 



13 In the highly developed ciliate, Paramecium, Woodruff recorded 600 generations 

 a year, but in bacteria Brefeld found two generations occur in an hour. Gray found 

 34 minutes to a generation in the trout's segmenting egg (1927, Brit. Journ. Exp. 

 Biol., iv. p. 315). 



