The threads produced by the hardening of the tenacious fluid exuded by these various animals were probably simply protective in origin. The curious caterpillar-like creature Peripatus spits out a viscid fluid when it is disturbed, which hardens into threads, and hopelessly entangles any small enemy which may venture to attack it. Threads of a poisonous nature are thrown out by jelly-fishes, polyps, and sea anemones, and serve them both as defence and as means of paralysing and capturing prey. A later stage in the use of such threads is their felting" to form a case or tube (as in the sea anemone called Cerianthus), and so their application has gradually developed to the formation of egg-cases, snares, and the wonderful web of the geometric spider, and the countless "flying-lines" of smaller spiders, which make up the mysterious thing we call "gossamer." 00 As to the limits of the tenuity of the threads of gossamer there are no direct observations. Probably they are often as fine as theth or 20th of an inch in diameter. The condensation of a very minute quantity of moisture on gossamer threads and spiders' webs no doubt helps to make them more readily visible to us in October weather than they are in full summer, when such moisture would not condense except in early morning or at sunset. It seems strange that man should have been unable to produce a thread so fine as that of the spider, but this reproach has now been removed. Spun glass is easily obtained 10th of a inch in diameter; but Mr. C. V. Boys, F.R.S., has, by fusing quartz (rock-crystal) by the oxy-hydrogen flame, and drawing it out by means of a small arrow (a straw), discharged from a bow-the near end of the arrow being adherent to a fused droplet of quartz which is held fast-produced threads of great strength and of extraordinary tenuity. The fineness can be regulated by the rapidity with which the drawing is effected. The threads are prepared (for use in suspending swinging bars in delicate measurements of force) of a thickness of 10,000th of an inch. Some have been made so fine as to be not only invisible to the naked eye, but to be only vaguely indicated by the highest powers of the microscope. They are estimated to be only one-millionth of an inch in diameter. It is difficult to form any mental picture or conception of these finest quartz threads spun by Mr. Boys. But the following fact helps us to realise how delicate they are. A grain of sand just visible to the eye -that is to say, th of an inch long, the same in breadth, and the same in height-would make twenty miles of such thread. 00 ΟΝ XXXII THE JUMPING BEAN NE way of thinking of the six hundred thousand kinds or species of insects-those tiny, ubiquitous fellow-creatures of ours which inhabit nearly every corner and cranny of the earth's surface-is to associate them with the plants upon which, either for food or protection, the greater number of them are dependent. This makes them appear less overwhelming in their astonishing and, at first sight, meaningless variety, than when one calls them to mind pinned out in long lines in innumerable drawers and cases, or assorted, like with like, in the wonderfully accurate and interminable pictures of them produced by those patient benefactors of mankind the systematic entomologists. Every plant of any size has a number of insects associated with it, living more or less completely on its substance, or making its home in some part of the plant. Some trees are known to have more than a hundred and fifty kinds or species of insects thus dependent on them, those which are vegetarian serving in their turn as food to a variety of carnivorous insects. The ways in which insects are associated with plants may be briefly stated. It must be remembered that often, though not always, one particular species of plant, and that only, is capable of serving the needs of a given species of insect. Thus, the leaves of a given plant are the necessary food of the grubs of one or more insects which bite their food; its internal juices serve others which suck; its roots others; its nectar in the flower others, which in return serve the plant by carrying away its pollen and fertilising the other plants of the same species which they visit. Protection is sought and obtained from the same plant by insects which burrow in its leaves, or roll them up, or cut them into slices and carry them away, or hide in its bark, or in the flowers, or in other parts-or burrow for food and shelter into its wood. Others lay their eggs in the soft buds, producing or not producing according to their kind distorted growths, known as "galls" (one plant is known to have as many as thirty species of gall-flies which make use of it). Other insects lay their eggs in the flower-buds and immature fruits, or place them on the plant so that the young grubs, when hatched, can at once eat into those soft parts. Others bore into the wood or into hard or fleshy fruits expressly to lay their eggs, or into the ripe seeds. Certain ants live in chambers specially provided by the woody parts of the plant for them, and benefit both themselves and the plant by devouring other insects which seek the plant in order to devour it. In a museum of natural history there should be exhibited at least one plant with specimens and enlarged models of all the insects which depend upon it for food, protection, or nursery, and with accompanying illustrations of the way in which those purposes are served. A curious product of the relationship of an insect and a plant is the so-called "jumping bean," which is brought to this country from Mexico, and may be purchased in some of the London shops which deal in "miscellaneous” articles. They have been known for some years, but are becoming now a regular article of commerce. As one buys them (Fig. 52) they are segments of a globular fruit which has divided into three, comparable to the familiar segments of an orange, but less numerous. They are about one-third of an inch long, light, quite dry, and apparently hollow, without any visible opening. Two sides of the little capsule are flat, and the third side is bulged and α FIG. 52. On the right two jumping beans; on the left the caterpillar removed from a jumping bean. The figures are a little larger than life-size, as is shown by the line drawn near the caterpillar giving its actual length. The shape of the "beans," as segments of a tripartite sphere, is seen. One shows a round hole, with a lid-like piece marked a, removed from the hole. This hole did not exist when the bean first came into my possession in November 1908. At that time the caterpillar within was active, and the bean or fruit-segment often jumped. In April the caterpillar cut this round hole from within, leaving the circular lid in place, and became a chrysalis. The lid was pushed out, as shown in the drawing, by the moth when it escaped from the chrysalis in July. (Drawn from nature for this work.) rounded, so that the capsule easily rocks when resting on that side. When these dry fruits or segments of a fruit are brought into a warm room or placed near a fire so as to make them as warm as the hand, they commence to rock and move with curious little jerks. They jump as much as one-eighth of an inch from the ground, and advance as much as a quarter of an inch at a time, though by rolling they may progress a good deal more. They will often move seven or eight times in the same direction so as to make a progress of a couple of inches on a flat surface. and I have found that if a cool surface or protection from warmth is within reach they will in the course of time arrive at that cool area and come to rest. When the plate on which they are placed becomes cool or the temperature of the room falls to what we should call "chilly," they |