84 SECTIONAL ADDRESSES. 



The lagoons of Solenhofen have preserved a strange mixture of land and 

 sea life, without a trace of fresh or brackish water forms. Archae- 

 opteryx, insects, flying reptiles, and creeping reptiles represent the air 

 and land fauna; jelly-fish and the crinoid Saccocoma are true open- 

 water wanderers ; sponges and stalked crinoids were sessile on the 

 bottom; starfish, sea-urchins, and worms crawled on the sea-floor; 

 king-crabs, lobsters, and worms left their tracks on mud-flats; cephalo- 

 pods swam at various depths ; fishes ranged from the bottom mud to the 

 surface waters. The Upper Ordovician Starfish bed of Girvan contains 

 not only the crawling and wriggling creatures from which it takes its 

 name, but stalked echinoderms adapted to most varied modes of life, 

 swimming and creeping trilobites, and indeed representatives of almost 

 all marine levels. 



In the study of such assemblages we have to distinguish between 

 the places of birth, of life, of death, and of burial, since, though these 

 may all be the same, they may also be different. The echinoderms 

 of the Starfish bed further suggest that closer discrimination is needed 

 between the diverse habitats of bottom forms. Some of these were, I 

 believe, attached to sea- weed; others grew up on stalks above the 

 bottom ; others clung to shells or stones ; others lay on the top of the 

 sea-floor ; others were partly buried beneath its muddy sand ; others may 

 have grovelled beneath it, connected with the overlying water by 

 passages. Here we shall be greatly helped by the investigations of 

 C. G. J. Petersen and his fellow-workers of the Danish Biological 

 Station. (See especially his summary, ' The Sea Bottom and its 

 Production of Fish Food,' Copenhagen, 1918.) They have set an 

 example of intensive study which needs to be followed elsewhere. By 

 bringing up slabs of the actual bottom, they have shown that, even in 

 a small area, many diverse habitats, each with its peculiar fauna, may 

 be found, one superimposed on the other. Thanks to Petersen and 

 similar investigators, exact comparison can now take the place of in- 

 genious speculation. And that this research is not merely fascinating 

 in itself, but illuminatory of wider questions, follows from the con- 

 sideration that analysis of faunas and their modes of life must be a 

 necessary preliminary to the study of migi'ations and geographical 

 distribution. 



The Tempo of Evolution. 



We have not yet done with the results that may flow from an analysis 

 of adaptations. Among the many facts which, when considered from 

 the side of animal structure alone, lead to transcendental theories with 

 Greek names, there is the observation that the relative rate of evolution 

 is very different in races living at the same time. Since their i-emains 

 are found often side by side, it is assumed that they were subject to the 

 same conditions, and that the differences of speed must be due to a 

 difference of internal motive force. After what has just been said you 

 will at once detect the fallacy in this assumption. Professor Abel has 

 recently maintained that the varying tempo of evolution depends on the 

 changes in outer conditions. He compares the evolution of whales, 

 sirenians, and horses during the Tertiary Epoch, and correlates it with 



