466 TRANSACTIGNS OF SECTION C. 
a conmimon rule that the prosperous and typical representatives are succes: 
sively larger and larger, as we see them in the familiar cases of the horses 
and elephants of the northern hemisphere and the hoofed animals and 
armadillos of South America. . 
Another frequent mark of old age in races was first discussed and clearly 
pointed out by the late Professor C. E. Beecher, of Yale. It is the 
tendency in all animals with skeletons to produce a superfluity of dead 
matter, which accumulates in the form of spines or bosses as soon as the 
race they represent has reached its prime and begins to be on the down- 
grade. Among familiar instances may be mentioned the curiously spiny 
Graptolites at the end of the Silurian period, the horned Pariasaurians at 
the beginning of the Trias, the armour-plated and horned Dinosaurs at the 
end of the Cretaceous, and the cattle or deer of modern Tertiary times. 
The latter case—that of the deer—is specially interesting, because fossils 
reveal practically all the stages in the gradual development of the horns or 
antlers, from the hornless condition of the Oligocene species, through the 
simply forked small antlers of the Miocene species, to the largest and most 
complex of all antlers seen in Cervus sedqwicki from the Upper Pliocene 
and the Ivish deer (C. giganteus) of still later times. The growth of these 
excrescences, both in relative size and complication, was continual and 
persistent until the climax was reached and the extreme forms died out. 
At the same time, although the paleontologist must regard this as a 
natural and normal phenomenon not directly correlated with the habits of 
the race of animals in which it occurs, and although he does not agree 
with the oft-repeated statement that deer may have ‘ perfected’ their 
antlers through the survival of those individuals which could fight most 
effectively, there may nevertheless be some truth in the idea that the growths 
originally began where the head was subject to irritating impacts and that 
they so happened to become of utility. Fossils merely prove that such 
skeletal outgrowths appear over and over again in the prime and approach- 
ing old age of races; they can suggest no reasons for the particular positions 
and shapes these outgrowths assume in each species of animal. 
It appears, indeed, that when some part of an animal (whether an 
excrescence or a normal structure) began to grow relatively large in succes- 
sive generations during geological time, it often acquired some mysterious 
impetus by which it continued to increase long after it had reached the 
serviceable limit. The unwieldy antlers of the extinct Sedgwick’s deer and 
Irish deer just mentioned, for example, must have been impediments rather 
than useful weapons. ‘The excessive enlargement of the upper canine teeth 
in the so-called sabre-toothed tigers (Machwrodus and its allies) must also 
eventually have hindered rather than aided the capture and eating of prey. 
The curious gradual elongation of the face in the Oligocene and Miocene 
Mastodons, which has lately*been described by Dr. Andrews, can only be 
regarded as another illustration of the same phenomenon. In successive 
generations of these animals the limbs seem to have grown continually 
longer, while the neck remained short, so that the head necessarily became 
more and more elongated to crop the vegetation on the ground. <A limit 
of mechanical inefficiency was eventually reached, and then there survived. 
only those members of the group in which the attenuated mandible became 
shortened up, leaving the modified face to act as a ‘proboscis.’ The 
elephants thus arose as a kind of after-thought from a group of quadrupeds 
that were rapidly approaching their doom. 
The end of real progress in a developing race of backboned animals is 
also often marked by the loss of the teeth. A regular and complete set of 
teeth is always present at the commencement, but it frequently begins to 
lack successors in animals which have reached the limit of their evolution, 
and then it soon disappears. Tortoises, for instance, have been toothless 
siuce the Triassic period, when they had assumed all their essential 
