316 
—gone, too, not only from Whittlesea, but from the whole world, 
is that most exquisite of English butterflies, Lycoena dispar, the 
Great Copper, and many an insect more !”—{ypp. go, gi.) 
The extinction of species is moreover foreshadowed in 
the case of those animals and plants which are becoming 
rarer and fewer from year to year. They are evidently 
doomed to disappear at no distant date, unless indeed 
the circumstances should alter and more favourable con 
ditions should be introduced. 
In considering the causes which have led to this ex 
tinction, we may first of all remark that there is a sense 
in which a species may be said to have become extinct, 
even when the race has continued to flourish. When all 
the members of a species undergo considerable modifica 
tion, the result may be denominated a new species, and 
the ancestral forms may be regarded as extinct species. 
The extinction of species in the more usual acceptation 
of that term may arise from various causes. In the first 
place, sudden and considerable change of external con 
dition, food, climate, will often prove fatal to a race. 
“The pre-existing structure of an organism prevents it from living 
under any new conditions except such as are congruous with the 
fundamental characters of its organisation—such as subject its 
essential organs to actions substantially the same as before. Great 
changes must kill it.”—(Herbert Spencer. The Principles of Biology, 
vol. i., p. 427.) 
“It is an everyday experience that changes in environment occur 
without any preparation for them on the part of living things. If the 
changes are very great, death is the result.”—(E. D. Cope. The 
Origin of the Fittest, p. 227.) 
“ By the breaking of an isthmus, and the consequent irruption of a 
multitude of new inhabitants into an adjoining sea, or by the final 
subsidence of an island, the process of extinction may have been 
rapid. ... In some cases the extermination of whole groups, as 
of ammonites towards the close of the secondary period, has been 
wonderfully sudden.”—(Origiti of Species, p. 2g4.)