
IN NATURAL HISTORY 11 
dependently in three widely separated parts of the world, and as they 
inhabit fresh water they could not have crossed the sea; it is also known 
that they belong to an old group of former wide distribution, their fossil 
remains being found in Europe and North America. So it is considered 
that at some very distant period of the world’s history there was a land 
connection between Australia, Africa, and South America, and that 
during this period the distribution of the Dipnoi took place, a conclu- 
sion that derives support from other evidence. 
Thus the life of the past has not only been continually changing, but 
has its bearing on that of the present time. As the world changed, new 
forms arose fitted to new conditions, race after race of animals came into 
existence, flourished for a time and then passed away, existing animals 
being those best adapted to live under present conditions. 
The story of the past life of the earth is usually considered by itself 
and that branch of science is termed Paleontology.! This is mainly a 
matter of convenience, because the subject is so great in itself, for the 
life of the past has its direct bearing on that of the present and to under- 
stand one it is necessary to have a knowledge of the other. 
NOMENCLATURE 
Some things about the study of natural history, or rather about the 
published results of this study, often seem peculiar and unnecessary, 
prominent among them being scientific names and the classification of 
animals, two matters that are intimately related. When men began 
really to study animals, and to publish the results of their observations, 
the descriptions were printed in Latin, this being the language used by 
students and familiar to men of liberal education in all countries. In 
order that the animals might be readily recognized, it was customary to 
preface the account of each with a brief description of its more evident 
characteristics, something much like what is now called a diagnosis. 
The lion, for example, might be styled the tawny colored cat with a mane; 
the tiger, the striped cat; the leopard, the large, many spotted cat, and 
soon. And to this day many naturalists preface their descriptions with 
a brief Latin diagnosis. As the tide of commerce of the eighteenth cen- 
tury brought to Europe scores of animals before unknown, the number of 
recognized species increased so rapidly that it became difficult to keep 
track of them. To overcome this difficulty, the great Swedish natural- 
ist, Linnzeus, devised the plan of giving to each animal two names, the 
1From the Greek palaios, ancient on, a being, and logia, to speak; in other words, a treatise on 
ancient beings or life. 
