682 THE FERTILIZATION OF FLOWERS BY INSECTS, ETC. 
small insects, something more than a large conspicuous corolla is 
required to show the visitors the way to the nectary or receptacle 
for the honey ; hence arises the variegation of flowers, the bands 
or patterns of color being almost invariably so arranged as to di- 
rect the insect in the way it should goin search of food. As na- 
ture seldom provides two contrivances, concurrently, for the same 
purpose, we find that variegated (wild) flowers are seldom scented ; 
while the most odoriferous flowers are-almost always uniform in 
color; the evening primrose, which opens its scented flowers only 
in the dusk, requires no variegation to direct the night-flying moths 
to the scented nectar. 
Illustrations of all these laws have been observed by the natur- 
alists we have mentioned, and have been collected with great in- 
dustry in this volume by Dr. Miiller, himself no idle worker in the 
same field. According to the theory of natural selection, those 
descendants from a common ancestor which vary from the others 
in any direction that tends to increase their attractiveness to insects, 
or to secure a more certain transference of the fertilizing pollen 
from one flower to another, will have the best chance of survival 
and of perpetuating and increasing this peculiarity in their prog- 
eny. Dr. Miller has himself examined, or records the observa- 
tions of others on, nearly four hundred species of plants, and 
describes the structure of the reproductive organs and of their en- 
velopes, with especial reference to their adaptation for self-fertili- 
zation or for cross-fertilization, giving in each case a list of all the 
insects which have been observed to visit the flower, and illustrating 
his description, where necessary, by admirable woodcuts. is 
portion of the subject is more or less familiar to most botanists ; 
what Dr. Müller has made peculiarly his own study is the tracing 
out of the same principle, applied to the visiting insects, as previ- 
ous observers have noted with respect to the visited flower. By the 
same principle of natural selection those insects which display to 
the greatest perfection contrivances for extracting the honey of 
flowers or for carrying away the pollen — the latter serving in some 
cases for their own food, in others for storing up in their nests a$ 
food for the larvee or young —will stand the best chance of perpet- 
uating offspring provided with the same peculiarities ; and we find 
here abundant descriptions and drawings of the various forms 
which these contrivances assume in different classes of insects. 
In his concluding chapter Dr. Müller discusses the origin of 
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