THE EVOLUTION THEORY 115 



primitive life far exceeded in length the time from the Cambrian 

 to the present day. 



That no certain traces of life from these earliest strata are 

 known to us need no longer surprise us. The longer the periods 

 elapsed, the greater the probability that these documents of 

 Nature perished, especially as we have to conceive the lowest 

 forms of life as ' lumps of slime ' without any skeleton parts, like 

 the existing microscopically minute Amoebae. 



The best instance of the inaccuracy of the older leaves of the 

 earth's chronicle is supplied by a comparison of the wealth of 

 forms found in the Silurian with that of the Cambrian Period. 

 From the latter we know only about six hundred or seven 

 hundred species, whilst from the Silurian strata over ten thou- 

 sand have been described. 



But if the earth's history does not elucidate the mystery of 

 the origin of life, it furnishes incontrovertible evidence of the 

 gradual development of the higher and highest organisms from 

 simple forms and for the transition of one species into another. 

 We need only once more recall the Archseopteryx, the evolution 

 of the horse, and finally the whole tendency expressed in the 

 evolution of the organic world. 



An equally convincing proof of the truth of the Evolution 

 Theory is supplied by Ontogeny, the history of the evolution of 

 the individual. Indeed, the development of most multicellular 

 animals proceeds during the earliest embryonic stages in such 

 remarkably uniform manner that we are only able to compre- 

 hend it on the hypothesis of a descent from a common ancestor. 

 For every animal passes in its development essentially through 

 all the stages which we observe permanently preserved in the 

 lower representatives of the same stem. Haeckel formulated this 

 fundamental law thus : " The evolution history of each animal, 

 its ontogeny, is a short recapitulation of its phylogeny ; i.e., the 

 principal stages of organization through which its ancestors 

 passed in remote ages are reproduced, though in a somewhat 

 changed form, in the development of each individual." 



But however clearly this law operates in numerous cases, 

 there are instances in which its application seems vague and 

 indistinct. The reason is that not only the adult individuals 

 exhibit new characters but that also all other stages are able to 



