2l6 THE FOUNDATIONS OF ZOOLOGY 



by these one hundred and forty-one species as it could be by a 

 collection from the bottom of the modern ocean. Four of the 

 American species are sponges, two are hydrozoa, nine are actino- 

 zoa, twenty-nine are brachiopods, three are lamellibranchs, thir- 

 teen are gasteropods, fifteen are pteropods, eight are Crustacea, 

 fifty-one are trilobites, and trails and burrows show the existence 

 of at least six species of bottom forms, probably worms or Crusta- 

 cea. The most notable characteristic of this fauna is the com- 

 pleteness with which these few species outline the whole fauna 

 of the modern sea-floor. Far from showing us the simple unspe- 

 cialized ancestors of modern animals, they are most intensely modern 

 themselves in the zoological sense, and they belong to the same 

 order of nature as that which prevails at the present day. 



The fossiliferous beds of the Lower Cambrian rest upon beds 

 which are miles in vertical thickness, and are identical in all their 

 physical features with those which contain this fauna. They 

 prove beyond question that the waters in which they were laid 

 down were as fit for supporting life at the beginning as at the 

 end of the enormous lapse of time which they represent, and 

 that all the conditions have since been equally favorable for the 

 preservation and the discovery of fossils. Modern discovery has 

 brought the difficulty which Darwin points out into clearer view, 

 but geologists are no more prepared than he was to give a satis- 

 factory solution, although I shall now try to show that the study 

 of living animals in their relations to the world around them does 

 help us, and that comparative anatomy and comparative embry- 

 ology and the study of the habits and affinities of organisms tel^ 

 us of times more ancient than the oldest fossils, and give a more 

 perfect record of the early history of life than paleontology. 



While the history of life as told by fossils has been slow and 

 gradual, it has not been uniform, for we have evidence of the 

 occurrence of several periods when modification was comparatively 

 rapid. 



We are living in a period of intellectual progress, and among 

 terrestrial animals cunning now counts for more than size or 

 strength, and fossils show that, while the average size of mam- 

 mals has diminished since the Middle Tertiary, the size of their 

 brains has increased more than one hundred per cent ; that the 



