110 THE ARREST OF THE BODY. 



types. While endless groups of plant and animal 

 forms have advanced during the geological ages, other 

 whole groups have apparently stood still — stood still, 

 that is to say, not in time hut in organization. If 

 Nature is full of moving things, it is also full of fix- 

 tures. Thirty-one years ago Mr. Huxley devoted the 

 anniversary Address of the Geological Society to a 

 consideration of what he called " Persistent Types of 

 Life," and threw down to Evolutionists a puzzle which 

 has never yet been fully solved. While some forms 

 attained their climacteric tens of thousands of years 

 ago and perished, others persevered, and, without ad- 

 vancing in any material respect, are alive to this day. 

 Among the most ancient Carboniferous plants, for in- 

 stance, are found certain forms generically identical 

 with those now living. The cone of the existing Arau- 

 caria is scarcely to be distinguished from that of an 

 Oolite form. The Tabulate Corals of the Silurian 

 period are similar to those which exist to-day. The 

 Lamp-shells of our present seas so abounded at the 

 same ancient date as to give their name to one of the 

 great groups of Silurian rocks — the Lingula Flags. 

 Star-fishes and Sea-urchins, almost the same as those 

 which tenant the coast-lines of our present seas, 

 crawled along what are now among the most ancient 

 fossiliferous rocks. Both of the forms just named, 

 the Brachiopods and the Echinoderms, have come 

 down to us almost unchanged through the nameless 

 gap of time which separates the Silurian and Old Red 

 Sandstone periods from the present era. 



This constancy of structure reveals' a conservatism 

 in Nature, as unexpected as it is wide-spread. Does it 

 mean that the architecture of living things has a limit 



