Palaeontology and the Biogenetic Law. 1 



PALAEONTOLOGY has long ceased to place itself exclusively at 

 the service of geology as the study of characteristic fossils. It 

 has gradually grown into an independent branch of the biological 

 sciences, and claims a share in all their movements and tendencies. 

 The conclusive establishment of the Doctrine of Descent has evoked 

 the most powerful revolution in descriptive natural history, influencing 

 and transforming its whole method of research. No large palaeonto- 

 logical work of to-day contents itself with the description of new 

 forms, the comparison of them with those already known, and the 

 arrangement of them in systematic order. To determine the genetic 

 relationships, the ancestry, the modification, and the further develop- 

 ment, in short, the race-history or phylogeny of the organisms under 

 consideration, is now regarded as essential, by many indeed as the 

 chief aim of palaeontology. 



As Darwin forcibly insisted, the doctrine of descent depends in 

 no small degree on palaeontological facts. Thus, the great similarity 

 of the fossils occurring in strata immediately superposed one on 

 another, e.g., the brachiopods, ammonites, and other molluscs, has 

 made it difficult for geologists to determine the age of sedimentary 

 rocks. In recent years a great number of closely-allied species have 

 been traced through several superposed beds, stages, or divisions of 

 formations, their exact morphological relationships have been studied 

 in the most careful manner, and J:hus the probability at least has 

 been established, that we are here dealing with a genealogical 

 sequence of blood-relations. To be sure these do not as a rule form 

 complete chains, wherein mutation is linked with mutation and species 

 with species. They are rather discontinuous series, of which all the 

 members change in a definite direction, and obviously form steps in a 

 line of development, which culminates in the last extinct or still- 

 existing representatives. Among the better-known series of forms I 

 will only refer to a few. The succession of genera, which leads from 

 Hyvacothevium — perhaps, indeed, from the five-toed Phenacodus — through 

 Paloplothevium, Auchilophus, Anchitherium, and Hipparion, to the single- 

 toed horse, forms one of the most quoted and most beautiful examples 



1 A paper read before the International Congress of Geologists, 1894. 



