2 
THE STUDY OF INSECTS, 
The diversity of forms of animal life is much greater than is com 
monly supposed. A competent authority has estimated that there 
are now living on the earth more than one million species of animals. 
And these are merely the surviving descendants of immense series 
of beings that have existed in past geological times, the remaining 
tips of a great genealogical tree, of which many twigs and branches 
have perished. 
The common figurative use of the word tree in this connection 
expresses well the convergence of the lines of descent toward the 
common ancestor from which existing forms have descended. But 
in one respect it may be misleading. If an ordinary tree be ex¬ 
amined, the tip of one branch will closely resemble that of any other 
branch of the same tree. But in this figurative genealogical tree 
we must imagine a very different state of affairs. Here the law of 
growth is constant change; each branch grows in its own individual 
way; and each twig of each branch bears fruit peculiar to itself. 
The changes, however, are gradual; and thus the tips of closely-con¬ 
nected twigs will be similar though not identical; while the tips of 
two branches that separated early in the growth of the tree will be 
very different. 
It is the effort of the systematist, one who studies the classification 
of animals and plants, to work out the relations which exist between 
the various tips of the genealogical tree. This study when carried 
to its fullest extent includes not only the study of existing forms of 
life, but also the study of those that have perished, the trunk-forms 
from which existing forms have descended. This, however, is a very 
difficult matter; and as yet only the beginnings of the Natural 
Classification have been made. See pp. 199 to 204. 
If we accept this theory of descent, now almost universally ac¬ 
cepted by naturalists, it is evident that when we take into account 
all the forms of life that have existed we cannot classify animals into 
well-marked groups; for as the modification in form is gradual,series 
of connecting links have existed between any two forms that might 
be selected. 
But practically the student that confines his attention to the 
study of living forms can classify these forms into more or less well- 
marked groups, for many of the connecting links have perished; in 
fact, the groups of living animals and plants are so distinct that it is 
only in recent years that naturalists have come to understand the 
blood-relationship referred to above. 
We find that the Animal and Vegetable Kingdoms are made up oi 
a vast assemblage of individuals, each the offspring of parents similar 
