264 
MEMBRA ClDJE. 
those on the neighbouring continents, perhaps they are even smaller. We may note 
also that the tropical examples of which we have experience, do not contrast 
unfavourably as to size with the more temperate species of N. America. 
With reference to migration of species, we may remember that, though New 
Zealand is nearer to Australia than to any other large district of land, yet their 
faunas are almost totally different. The migration of insects (which are on the 
whole vegetable feeders) may be safely said to follow the lines of distribution of the 
plants on which they feed. But Huxley, speaking of the flower gentian, sa} r s that 
migration of animals helps nothing as between the Old World and the South American 
flora. Yet in some way the tapirs of the Andes are connected with the tapirs of the 
Malay peninsula, though vast oceans intervene. How did they cross these oceans P 
It is almost impossible to foresee the effects of a superabundant popular increase 
of man as to the spread of animals over the earth. His scientific activity interferes 
with the struggle of the fittest, and tends to the extirpation of those animals which 
he considers may interfere with his own special economy. 
But easy locomotion also introduces pests and disease, such as murrains and 
pibrine, phyloxera and coccus-scale, and the winds even spread “ contagions ” and 
scatter unwelcome germs, which tend to restore the natural balance of life, which 
has for a time been interfered with by man. 
We may regret that as useful flocks and herds increase, the interesting creatures 
of olden times tend to diminish and pass away, never to return. 
A dull utilitarian, mechanical age seems to be taking the place of variation, and 
even affecting the ethics of true art. Yet though “ many shall run to and fro, and 
knowledge shall increase,” all is not on the side of extinction. Flowers and beasts 
appear in new places where they have not been known as indigenous, and landscape 
has still its charm for those who will see its beauty. 
It will be noticed that the ^Ethalionidse and the Machaerotidae are not included in 
the order of this Monograph. Though they are closely allied to the Membracida?, 
through the Cercopidae, or through the Jassidae, they want certain distinctive charac¬ 
ters of the family, which justify their omission. 
