90 ORGANIC EVOLUTION CONSIDERED 



organized. Nor is the fauna a meagre one in number 

 of species. In the United States and Canada alone 

 about 200 species are already known, of which nearly 

 100 are trilobites."* 



Again he says: "At the end of the Archaean times 

 — when the Archaean volume closed — we find only the 

 lowest protozoan life. But with the opening of the 

 next era, apparently with the first pages of the next 

 volume, we find already the great types of structure 

 except the vertebrata. And these not the lowest of 

 each type, as might have been expected, but already 

 trilobites among Articulata, and Cephalopods among 

 Mollusca — animals which can hardly be regarded as 

 lower than the middle of the animal scale." 



As an explanation of this remarkable condition of 

 things, of this sudden appearance in the geological 

 record of so many and such highly organized forms of 

 animals, we are told that "We must remember that 

 between the Archaean and Paleozoic there is a lost 

 interval of enormous duration," and that during this 

 interval the above named numerous forms were x 

 evolved from simple Archaean forms; that this lost 

 interval was long enough to evolve trilobites and 

 cephalopods "which can hardly be regarded as lower 

 than the middle of the animal scale," from the proto-, 

 zoa of the Archaean. 



Here are two great classes of animals, complex in 

 structure, — the trilobite possessing well-developed 

 compound eyes, and the cephalopod having simple 

 eyes, that closely approach in complexity the eyes of 

 man. The cephalopods are probably the most highly 

 organized of the invertebrates. They possess two- 

 eyes, a beak much like that of a parrot reversed in 

 position, two or four gills — the ancient ones had 

 four gills, — a distinct alimentary canal, with a well 



* Elements of Geology, p. 297. * Ibid, p. 298. 



