CREATION BY EVOLUTION 



slate of Lower Cambrian age, the most marvellous impres- 

 sions of delicate and fragile organisms have been found — 

 mere films of carbon against the slate — ^with all their detail of 

 structure preserved with the utmost fidelity. These impres- 

 sions show many of the relatively high invertebrate types, 

 such as worms, crustaceans, and echinoderms, and here there 

 might well be preserved the ancestral stock out of which the 

 backboned creatures arose, although, so far as actual dis- 

 covery goes, that record is much later in time. 



Except for a persistent type of being variously known as 

 Amph'ioxus or Branchiostoma, which to this day inhabits the 

 shallow waters bordering the continents, there is again no 

 trace of the important link connecting the vertebrates with 

 their invertebrate forebears. To those of us who are prehis- 

 torically interested this is perhaps the most coveted of all 

 the missing links, for its discovery will help to settle argu- 

 ments that have arisen in favor of this or that method of 

 origin, about which so little is really known. 



In Silurian time there came the sharks, known largely 

 from their fossil teeth, some so much like the teeth of mod- 

 ern persistent survivors that the external form and habits of 

 life of some of the early species may be safely surmised by 

 analogy, although others are unlike any that now exist. Of 

 their gradual evolution, especially in the favored lines 

 which were to produce the higher fishes, sufficient, perhaps, 

 is known. Out of one armored group, however, there were 

 to arise the land-living vertebrates. Here again there is 

 more hypothesis than observed fact, and especially desirable 

 would be the discovery of fishes whose fins show potentiali- 

 ties, either in their structure or their implied use, or both, of 

 giving rise to the shore-adapted foot, the point of departure 

 of all terrestrial progression. There is at Yale a single foot- 

 print, which speaks volumes to those who read its lesson 



[258} 



