THE LIVING WORLD. 
19 
further maintained that there has been an uninterrupted succession in the 
animal kingdom effected by means of generation, from the earliest ages of 
the world to the present day; that new species and transformations have 
been gradually produced by the growth of new parts, originating from certain 
efforts -of the animal to fulfil particular instincts, such as the foot of a bird 
becoming webbed from repeated efforts to swim; and that the ancient animals 
which we find in a fossil state, however different in structure they may be, 
were in fact the ancestors of those now living. 
In the theories here advanced, I claim no originality, as the facts thus 
briefly stated constitute a highway over which many writers have preceded me. 
But they are always interesting and instructive, and I have used them in order 
to more clearly, define the plan upon which the Living World has been con¬ 
structed, iu which respect there is a departure from the basis of all other natural 
histories that I have consulted. I beg especially to refer the reader to the 
Introduction, in which I have endeavored to explain, generally, the objects 
and basis of this work, and which will be serviceable to the reader to know. 
fossil moll cjs k from Silurian strata {Slimonia acuminated). 
Having thus hastily glanced at the primitive condition of the globe and the 
probable mutations through which it has passed, my purpose now is to describe, 
as best I can, the animal life with which we are most familiar, using the word 
animal in a specific sense, to designate creatures that have powers of locomotion 
and sensibility highly developed, as contradistinguished from what is called the 
protozoan, or lowest order of animal creation. Nor do I esteem it as being of 
practical importance to include in this work descriptions of such animals of 
minute size as are rarely met with, but rather to confine myself to those 
creatures, the nobler animals, that subserve a useful purpose in the economy 
of nature most readily comprehensible by the mind of the average reader and 
thinker. But having in view the idea of acquainting my readers, by practical 
illustration, with the theory of the development of species, I have thought it 
appropriate to include here, in the early pages of this work, descriptions of 
some of the representative types of the lower orders of creation, by which it 
will be more readily discovered upon what hypothesis the theory of development 
is based. Passing over, therefore, microscopic organism, we reach the clasf; 
roming thereafter which has been called, though not with any definiteness, 
