262 
Notices of Books, 
[April, 
therefore feel little surprise if, under circumstances mainly simi- 
lar, we can perceive no modification, even during such long 
periods of time. Further, the sea does not absolutely prevent 
the passage of insects from the Continent to England. Hornets, 
wasps, winged ants, &c., may cross a strait of 20 miles in 
breadth as readily as butterflies and locusts, both of which have 
been known to fly much greater distances. We may further 
point to distinct instances where “ instincts ” have been found 
capable of variation, and where changes have been made in ac- 
cordance with modifying circumstances. In a book which is in 
the hands of every naturalist* we find instances of alterations 
and improvements in the nests of birds. 
Prof. Heer maintains that “ if instinct were the result of 
education it would at the same time be capable of attaining per- 
fection, and, in the case of insects gifted with the most wonder- 
ful instindts, changes might be expedted more rapid in conse- 
quence of the very limited period of individual existence of each 
insect.” Now, this “very limited period of individual existence” 
is, we maintain, precisely the reason why changes are so slow. 
The longer any animal lives the greater opportunity it has to 
profit by experience, and the more probability there is that its 
fellows can observe and profit by any improvement upon which 
it may have come. If we consider how slow has been the pro- 
gress of man — how often even the most highly-organised varieties 
of our species have been at a stand-still, or even retrogressive — 
need we wonder that in animals far lower the movement may 
escape our observation ? 
Prof. Heer considers that we are still in the dark as to the 
fundamental conditions of the transformation of types which he 
admits to have taken place. Believing the changes to be sudden 
instead of gradual, he approximates to the position of Prof. 
Mivart. 
The following passage from the Editor’s Preface should not 
be overlooked : — 
“ In Ancient Tertiary strata the chestnut ( Castanea atava) had 
leaves distinctly toothed, but devoid of any points, and from the 
primary vein of the leaf curved secondary veins sprang at a 
distance from each other. 
“ In the Middle Tertiary strata the secondary veins of the 
chestnut leaf approximated to one another, and teeth protruded 
and were more numerous. 
“ In the latest Tertiary strata the secondary veins of the 
chestnut leaf were still nearer to each other, and almost recti- 
linear, while the teeth of the leaf had become set with thorns, 
as in the sweet chestnut ( Castanea , oesca ) of our own times.” 
Is not this a striking case of that gradual transformation 
which Prof. Heer is unwilling to recognise ? 
* Wallace, on Natural Selection, pp, 224 to 230* 
