(33 INTRODUCTION. 
entific certainty and exactness require characters which 
are not liable to dhange, and which we can seek only 
in the organization of the animal. This alone remains 
always the same ; for notwithstanding the speculations 
of M. Lamarck and his followers, there is not a shadow 
of evidence tending to prove the slightest permanent 
change, in the structure of a single animal, since the 
creation of the world. Species, genera, and even whole 
groups of animals have been created, and have be- 
come extinct ; but, so far as we know, the organization of 
the most insignificant species has undergone no change. 
The permanent characters drawn from this source, 
combined with those of the shell, will enable us success- 
fully to discriminate between species, and we may ob- 
tain collateral aid from the observation of then struc- 
tural functions, their instincts, and their habits ; and 
thus, while seeking to exhibit their distinctions alone, 
may do much towards completing their natural history. 
The requirements of science can no longer be satisfied 
by a single Linnasan phrase ; the characteristics of the 
whole organized being are needed ; and the description 
of the shell alone, ought never to be admitted, except 
when that of the animal itself cannot be obtained. The 
naturalist who has it in his power to acquire a know- 
ledge of the annual, as well as of the shell, should be 
held in every case so to do, and to make both known 
together. 
Conchology, considered as the study of the imper- 
ishable portions of a class of animals, has been, and 
