PRESIDENTIAL ADDRESS. 465 
to a large size. ‘There was no transition, for instance, between the reptiles 
of the Cretaceous period and the mammals which immediately took their 
place in the succeeding Eocene period: those mammals, as we have seen, 
had actually originated long ages before, and had remained practically 
dormant in some region which we have not yet discovered, waiting to burst 
forth in due time. During this retirement of the higher race the reptiles 
themselves had enjoyed an extraordinary development and adaptation to 
every possible mode of life in nearly all parts of the globe. We do not 
understand the phenomenon—we cannot explain it; but it is as noticeable 
in the geological history of fishes as in that of the land animals just con- 
sidered. It seems to have been first clearly observed by the distinguished 
American naturalist, the late Professor Edward D. Cope, who termed the 
sudden fundamental advances ‘expression points,’ and saw in them a 
manifestation of some inscrutable inherent ‘ bathmic force.’ 
Perhaps the most striking feature to be noticed in each of these ‘ expres- 
sion points’ is the definite establishment of some important structural 
character which had been imperfect or variable before, thus affording new 
and multiplied possibilities of adaptation to different modes of life. In 
the first lung-breathers (Stegocephala), for example, the indefinite paddle 
of the mud fishes became the definite five-toed limb; while the incomplete 
backbone reached completeness. Still, these animals must have been con- 
fined almost entirely to marshes, and they seem to have been all carnivorous. 
In the next grade, that of the reptiles, it became possible to leave the marshes ; 
and some of them were soon adapted not only for life on hard ground or 
in forests, but even for flight in the air. Several also assumed a shape of 
body and limbs enabling them to live in the open sea. Nearly all were 
carnivorous at first, and most of them remained so to the end; but many 
of the Dinosaurs eventually became practically hoofed animals, with a 
sharp beak for cropping herbage, and with powerful grinding teeth. In 
none of these animals, however, were the toes reduced to less than three in 
number, and in none of them were the basal toe-bones fused together as they 
are in cattle and deer. It is also noteworthy that the brain in all of them 
remained very small and simple. In the final grade of backboned life, 
that of the mammals, each of the adaptive modifications just mentioned 
began to arise again in a more nearly perfected manner, and now survival 
depended not so much on an effective body as on a developing brain. The 
mammals began as little carnivorous or mixed-feeding animals with a 
small brain and five toes, and during the Tertiary period they gradually 
differentiated into the several familiar groups as we now know them, 
eventually culminating in man. 
The demonstration by fossils that many animals of the same general 
shape and habit have originated two or three times, at two or three succes- 
Sive periods, from two or three continually higher grades of life, is very 
interesting. To have proved, for example, that flying reptiles did not pass 
into birds or bats, that hoofed Dinosaurs did not change into hoofed 
mammals, and that Ichthyosaurs did not become porpoises; and to have 
shown that all these later animals were mere mimics of their predecessors, 
originating independently from a higher yet generalised stock, is a remark- 
able achievement. Still more significant, however, is the discovery, that 
towards the end of their career through geological time totally different 
races of animals repeatedly exhibit certain peculiar features, which can 
only be described as infallible marks of old age. 
The growth to a relatively large size is one of these marks, as we observe 
in the giant Pterodactyls of the Cretaceous period, the colossal Dinosaurs 
of the Upper Jurassic and Cretaceous, and the large mammals of the 
Pleistocene and the present day. It is not, of course, all the members of 
a race that increase in size; some remain small until the end, and they 
generally survive long after the others are extinct; but it is- nevertheless 
1909. HH 
