PL.ESIDENTIAL ADDRESS. 4.69 
@ successive series of individuals and species obtained from the different 
layers of one geological section ; but even now I do not think we can do much 
better than our predecessors in unravelling real genealogies. At least Pro- 
fessor Depéret’s genealogical table of the Lower Tertiary pig-like Anthra- 
cotheriide, which he publishes as an illustration of ‘ évolution réelle,’ seems 
to me to be no more exact than several tables of other groups by previous 
authors which he criticises. His materials are all fragmentary, chiefly jaws 
and portions of skulls; they were obtained from several isolated lake- 
deposits, of which the relative age cannot be determined by observing the 
geological superposition ; and they represent a group which is known to 
have lived over a large part of Europe, Asia, Northern Africa, and North 
America. There is therefore no certainty that the genera and species 
enumerated by Professor Depéret actually originated one from the other in 
the region where he happened to find them ; he has demonstrated the general 
trend of certain changes in the Anthracotheriidw during geological time, but 
really nothing more. 
Eyen when a group of animals seems to have been confined to one com- 
paratively small region, where the series is not complicated by migration to 
and from other parts of the world, modern research still emphasises the 
difficulty of tracing real lines of descent. The primitive horned hoofed 
animals of the family Titanotheriide, for example, are only known from 
part of North America, and they seem to have originated and remained 
there until the end. As their fossil skeletons are abundant. and well 
preserved, it ought to be easy to discover the exact connections of the 
several genera and species. Professor Osborn has now proved, however, that 
the Titanotheres must have evolved in at least four distinct lines, adapted 
‘for different local habitat, different modes of feeding, fighting, locomotion, 
&c., which took origin, in part at least, in the Middle or Upper Kocene.’ 
They exhibit ‘four distinct types in the shape and position of the horns, 
correlated with the structure of the nasals and frontals, and indicative of 
different modes of combat among the males.’ The ramifications of the group 
are indeed so numerous that the possibility of following chains of ancestors 
begins to appear nearly hopeless. 
Among early reptiles the same difficulties are continually multiplied by 
the progress of discovery. About twenty years ago it began to appear likely 
that we should soon find the terrestrial ancestors of the Ichthyosauria in the 
Trias; and somewhat later a specimen from California raised hopes of 
obtaining them by systematic explorations in that region. During more 
recent years Professor J. C. Merriam and his colleagues have actually made 
these explorations, and the result is that we now know from the Californian 
Trias a multitude of reptiles, which need more explanation than the 
Ichthyosauria themselves. Professor Merriam has found some of the links 
predicted between Ichthyosaurs and primitive land reptiles, but he has by 
no means reached the beginning of the marine group; and while making 
these discoveries he has added greatly to the complication of the problem 
which he set out to solve. 
Serious difficulties have also become apparent during recent years in 
determining exactly the origin of the mammals. For a long time after the 
discovery of the Anomodont or Theromorph reptiles in the Permian-Trias 
of South Africa, it seemed more and more probable that the mammals arose 
in that region. Even yet new reptiles from the Karoo formation are con- 
tinually being described as making an astonishingly near approach to 
mammals; and, so far as the skeleton is concerned, the links between the 
two grades are now very numerous among South African fossils. Since these 
reptiles first attracted attention, however, they have gradually been found in 
the Permian and Trias of a large part of the world. Remains of them were 
first met with in India, then in North America, and next in Scotland, while 
during the last few years Professor W. Amalitzky has disinterred so many 
