an insect must exist in its native country (Madagascar) with a proboscis long enough to reach to the bottom of the nectary; and, quite recently, this has been proved to be actually the case. The geographical limits of the natural distribution of many plants are again fixed rather by the distribution of the insects which fertilise them than by the climatic requirements of the plants themselves. Local botanists state that in this district of South Lancashire many wild plants are not found, or only very rarely, which are extremely abundant with us in the south of England, such as the Laminum album, or White Dead-Nettle, the Convolvulus arvensis, or Smaller Bindweed, the absence of which can only be accounted for on similar grounds, there being nothing in the climate or soil to prevent their occurrence. One of your best local botanists, Mr. Grindon, states that the fragrant Labiates (every Labiate, in fact, that yields powerful odour) are wanting, except Stachys sylvatica, and the Wild Thyme in one or two very rare localities. The white Dead-Nettle, the HoundsTongue, the Sweet Violet, the Plantago media, all among the commonest of common plants in the southern countries, are here all but entirely absent. The two common Mallows are very rarely seen, the common Bindweed never; the Cowslip is extremely local; the Comfrey is unknown, as also is the commonest of the Wild Poppies. On the other hand, some splendid plants, like the Giant Bell Flower Campanula latifolia, hardly known in the south, are here very common. As you travel from a more southern clime northwards, one class after another of insects disappears, and with them the plants which depend on them for their fertilisation. In Alpine and Arctic countries a number of the native plants, especially the trees like the Birch and the Fir, have very inconspicuous flowers, and are exclusively wind-fertilised; while others have remarkable brightly-coloured or powerfully-scented flowers, like the Rhododendron, or Alpine Rose, and the beautiful Soldanella and Gentian, which thrust their brilliant sky-blue flowers even through the melting snow, to attract from great distances the comparatively rare insect visitors. Every traveller has remarked the brilliancy of the Alpine flora in May or June, or of that of a country where the flowering season lasts for only a very few weeks, like Palestine; but few have probably speculated on any other reason for this than the egotistic idea that its only purpose was to gratify the eye of the passing traveller. Darwin, in his "Origin of Species by Means of Natural Selection," gives a curious instance of the mode in which these different forms of life are inextricably intermingled with one another. The common Red Clover is visited and fertilised only by humble-bees, the proboscis of the honey-bee not being long enough to reach the nectar. The number of humble-bees in any district depends in a great measure on the number of field-mice, which destroy the combs and nests. The number of field-mice is again largely dependent on that of cats; and the nests of humblebees are therefore especially abundant near towns and villages where cats abound. Hence it may be said, without exaggeration, that to our domestication of the cat is due, to a large extent, the possibility of large clover crops. The function of fertilising flowers is not absolutely confined to insects in the animal world; spiders and snails also do their part, though to a comparatively small extent. In tropical, and even in temperate America, a large part of this duty is done by hummingbirds, which live on the honey obtained from the very long and deep tubes of such flowers as the Bignonia, or Trumpet-Flower. Some very curious relationships have been drawn out between the length of the beak of each species of humming-bird and that of the tube of the flower from which it chiefly obtains its food. Humming-birds are also said to have a penchant for brilliant scarlet flowers, which are very common in tropical countries, while the colour is very rare among the natives of temperate climates. Among our common wild flowers it would be difficult to name any of this hue, except the Poppy and the little Scarlet Pimpernel. But there is another important feature in special adaptation for insect fertilisation on which we have not yet touched; and this refers to the variegation of flowers. The large flowers of which we have at present spoken as being chiefly fertilised by insects of the largest kind have been uniform in colour without any variegation, as the Wild Rose, the large White Convolvulus, the Pœony, and the Evening Primrose. There are a large number of other flowers, both larger and smaller, which owe their beauty to variegation, that is, to dots or streaks of a different colour to that of the greater part of the petals. It was pointed out as long ago as by K. C. Sprengel, the botanist of last century to whom I have already alluded, that whatever variegated plant you observe, say the Fritillary, the Mimulus, the Pelargonium, or the Pansy, the streaks or dots will invariably be found pointing towards the nectary, or receptacle of honey; and that, moreover, brightly variegated plants are almost invariably scentless. The conclusion was irresistible, a conclusion abundantly confirmed by observa. tion, that the variegation is a guide to insects in search of the food in those large flowers in which the guide derived from odour is wanting It has also been observed, as might also have been expected, that variegated flowers are very commonly visited and fertilised by very minute insects, by whom such a guide-post is especially wanted. A very instructive lesson in Nature's economy of resource in not supplying in the same instance two means to the same end, may be learnt by contrasting a number of pairs of nearly-related plants; in each case one having uniform-coloured scented, and the other variegated scentless flowers, as the Primrose and the Auricula, the Sweet Violet and the Pansy, the Musk and the Mimulus, the Sweet-scented Orchis (O. Conopsea) and the Spotted Meadow Orchis, and many others. In the Wild Pansy (Viola tricolor) we have a remarkably good instance of the special contrivances intended to aid small insects in their search for honey. The nectary is, in this case, the extremity of two remarkable appendages, which hang down from two of the stamens into the "spur" of the corolla. Of the five petals, the lower and the two side ones have streaks pointing to the orifice in the centre of the flower. When an insect gets inside this opening, it finds it completely blocked up by a ring formed of the five anthers, except just in front, where there is a small opening just large enough to admit its body. Exactly opposite this opening is the thicker end of a wedge-shaped black streak, which conducts the insect right down the style to the very spot where it can reach the nectary. In making the descent, it must necessarily carry off some of the pollen which is discharged from the stamens internally within the ring; and in making the ascent and emerging from the small orifice, it must also, almost inevitably, enter the stigma, which is here a cavity in the upper part of the style, above the ring formed by the stamens. As far as my own observation goes, the Wild Pansy is fertilised only by the Thrips, one of the minutest of insects; but the interesting point is, that both the little opening in the anther-ring and the black streak on the style are wanting in the Sweet Violet, where they are not required, and where fertilisation is effected in quite a different way. In the few illustrations of my subject which I have been able to bring before you this evening, I trust that I have been able to show you that even in such an apparently simple operation of nature as the fertilisation of the flower, there is a boundless field for careful observation-observation that will amply repay, in the evidence it will yield of the most beautiful adaptation of purpose to end-of the inexhaustible wealth of contrivance by which every living creature is enabled to fit itself to the special circumstances in which it is placed, and thus indirectly to assist in the harmonious working of the whole of which it forms a unit. There is no pursuit more easily accessible to dwellers in the country than the observation of facts connected with vegetable physiology; no field in which there is still more left to be explored by any careful worker. "The more I study Nature," says Darwin, "the more I become impressed, with ever-increasing force, with the conclusion, that the contrivances and beautiful adaptations slowly acquired through each part, occasionally varying in a slight degree but in many ways, with the preservation or natural selection of those variations which are beneficial to the organism under the complex and ever-varying conditions of life, transcend in an incomparable degree the contrivances and adaptations which the most fertile imagination of the most imaginative man could suggest, with unlimited time at his disposal." And if I may be allowed to say so, in the presence of such an audience as this, to those who dwell in towns (especially those whose employment is the monotonous one of daily mechanical labour), there is no holiday pursuit, no recreation, better adapted to cultivate those faculties of the mind which are not employed in your daily labour; to preserve that even balance of all the mental powers which marks the wise and large-minded man, than the study of the ways of Nature, the examination of those laws, which, in their unvarying constancy, and yet their constant variety, raise us so far above the petty details of our daily life, and teach us that we ourselves also are a part of this stupendous whole; that on our own conduct, on our performing those duties in the world for which we are adapted, even if they appear to be as unimportant as those of the insect visiting the flower, depends the fulfilling of our part in preserving the harmony of the universe. That great and true lover of Nature, the poet Wordsworth, said To me the meaner flower that blows does bring But it requires more than an ordinary appreciation of the harmony of Nature's laws to be able to say with Tennyson Flower in the crannied wall, I pluck you out of the crannies: Parasites, and their Strange Uses. A LECTURE, Delivered in the Memorial Hall, Manchester, on Wednesday, November 12th, 1873. By T. SPENCER COBBOLD, Esq., M.D., F.R.S. ADIES AND GENTLEMEN,-Lest the subject of my discourse this evening should have alarmed some of you who may not unnaturally entertain a horror of parasites and parasitism, I wish to remark at the outset that the study of these creatures is of the highest interest, and really quite attractive. It is attractive because it is full of novelty; yet more attractive because the study opens up to our view some of the strangest biological phenomena of which the human mind can take cognisance; and yet most attractive in this utilitarian age because a knowledge of it brings with it a rich reward practically, enabling us to do effectual battle with some of the many ills of life to which our human flesh is heir. I would have you observe that in order to acquire a satisfactory knowledge of this subject, indeed to be enabled to interpret aright any of Nature's secrets, you must allow me to say-enter upon all such studies in a right frame of mind. The prime requisite in the study of this subject is a matter of personal and moral discipline. This discipline consists in a rigorous determination on the part of the student to dispossess his mind of all preconceived opinions whatsoever, and in an attitude of child-like simplicity to seek truth only for truth's sake. Those people who with nervous anxiety are for ever seeking to reconcile the conclusions of modern science with the ideas of their forefathers are likely to remain just as ignorant of the true value and significance of Nature's teachings or |