610 THE SPIEAL SHELLS [ch. 



at least escaping, the dangers of concussion. But this is after 

 all a very simple matter of mechanical analysis. The coarseness 

 or fineness of the sediment on the sea-bottom is a measure of the 

 current : where the current is strong the larger stones are washed 

 clean, where there is perfect stillness the finest mud settles down ; 

 and the hght, fragile shells of the Foraminifera find their appro- 

 priate place, hke every other graded sediment, in this spontaneous 

 order of hxiviation. 



The theorem of Organic Evolution is one thing; the problem 

 of deciphering the fines of evolution, the order of phylogeny, the 

 degrees of relationship and consanguinity, is quite another. Among 

 the higher organisms we arrive at conclusions regarding these 

 things by weighing much circumstantial evidence, by dealing with 

 the resultant of many variations, and by considering the probabifity 

 or improbabihty of many coincidences of cause and effect; but 

 even then our conclusions are at best uncertain, our judgments 

 are continually open to revision and subject to appeal, and all 

 the proof and confirmation we can ever have is that which comes 

 from the direct, but fragmentary evidence of palaeontology*. 



But in so far as forms can be shewn to depend on the play of 

 physical forces, and the variations of form to be directly due to 

 simple quantitative variations in these, just so far are we thrown 

 back on our guard before the biological conception of consan- 

 guinity, and compelled to revise the vague canons which connect 

 classification with phylogeny. 



The physicist explains in terms of the properties of matter, 

 and classifies according to a mathematical analysis, all the drops 

 and forms of drops and associations of drops, all the kinds of 

 froth and foam, which he may discover among inanimate things ; 

 and his task ends there. But when such forms, such conformations 

 and configurations, occur among living things, then at once the 

 biologist introduces his concepts of heredity, of historical evolution, 

 of succession in time, of recapitulation of remote ancestry in 

 individual growth, of common origin (unless contradicted by 

 direct evidence) of similar forms remotely separated by geo- 

 graphic space or geologic time, of fitness for a function, of 



* In regard to the Foraminifera, "die Paiaeontologie lasst uns leider an Anfang 

 dej Stammesgeschichte fast ganzlich im Stiche," Rhumbler, op. cii., p. 14. 



