It is a somewhat remarkable fact that the domain of human existence is singularly liable to be intruded upon by lower forms of both animal and plant life, which may in some cases inflict injury of great extent upon man’s possessions or even upon his bodily frame. Not so long ago a foreign member of the beetle-fraternity threatened the interests of agriculturists in this country, and caused consternation to prevail throughout the length and breadth of the land. And although the alarm with which the advent of the insect-intruder was hailed has now disappeared, agriculturists would inform us that their especial territory is beset with other insect-enemies which invariably damage their crops, and which in certain seasons cause the disastrous failure of many a thriving field. Witness in proof of this the ravages of the ‘turnip-fly’ and its neighbours, which blight the crops in some districts to an extent which must be seen to be realised. Or take the case of the hop-grower, whose favourable prospects largely depend on the absence of a small species of plant-lice which specially affects these plants, and which in certain seasons may cause, by their enormous increase, the total failure of this important crop. Nor do our insect-foes confine their ravages to growing-crops. When the fruits of the harvest have been duly gathered in and stored within the granary, even there they are attacked by minute pests. Numberless insects—flies, beetles, and other forms—select the granary as a nursery or suitable place for the upbringing of their young; the larvæ or young insects feeding on the grain and destroying large quantities by their increase as well as by their destructive habits. Apart from the domain of agriculture, however, lower forms of animal and plant life powerfully affect man’s estate. The growth and increase of lower plants produce many skin-diseases; and if it be true—already rendered probable—that epidemics are propagated through the agency of living ‘germs’ which increase after the fashion of lower forms of life, then it may be held that we are liable to be attacked on every side by enemies, insignificant as to size, but of incalculable power when their numbers are taken into consideration. Parasites of various kinds ravage man’s flocks and even affect his own health, so that it is perfectly clear that we do not by any means enjoy any immunity whatever from the enemies which living nature in its prolific abundance produces, and which select man and man’s belongings as their lawful spoil.