"In these five species" (in which the viscid matter “is so adhesive that it serves to attach the pollinia firmly to the insects without getting hard "), "and in these alone, we find copious nectar ready stored for rapid suction in open nectaries. On the other hand, whenever the viscid matter gets hard by exposure for a short time to the air, it would manifestly be advantageous to the plant if insects were delayed in obtaining the nectar; and in all such species the nectar is lodged within intercellular spaces, so that it can be obtained only by the inner membrane being penetrated at several points, and this will require time. If this double relation is accidental, it is a fortunate accident for the plants; but I cannot believe it to be so, and it appears to me one of the most wonderful cases of adaptation which has ever been recorded." Some orchids secrete instead of nectar a clear liquid like water. This fluid is collected in a petal inserted at the lower part of the flower and shaped into a deep cup-shaped receptacle. It does not attract insects, but by wetting their wings compels them to leave the flower by a different exit which passes close to the reproductive organs (i.e., the anther and the stigma). The soft linings of the cup are greedily devoured by certain insects, particularly by bees. Dr. Cruger, who observed this, has often seen bees fall into the cup whereupon their wings became so wet as to prevent their flying away, and they have been obliged to get out by the channel that carries off the waste from the reservoir. As the saturated bees creep along the narrow passage after their involuntary immersion, they come inevitably in contact with the stigma and the masses of pollen. The latter adhere to the bodies of the bees and can be conveyed to the sticky stigma of a neighbouring flower. ir In other orchids (Catasetum, Fig. 1), the male elements are discharged by a spring-like arrangement on the body of insects. When certain parts of the flowers are touched, the pollinia are thrown off like arrows, which, in the place of the barbs, have viscid swellings. "The insect, disturbed by so sharp a blow, or after having eaten its fill, flies sooner or later away to a female plant and, whilst standing in the same position as before, the pollen-bearing end of the arrow is inserted into the stigmatic cavity, and a mass of pollen is left on its viscid surface." * After giving detailed descriptions of the cross-fertilisation of flowers by such peculiar means, Darwin makes the following remark: "Who would have been bold enough to have surmised that the propagation of a species depended on so complex, so apparently artificial, and yet so admirable an arrangement ? " † One orchid (Herminium monorchis, Fig. 2), which bears very small flowers, is remarkable for the way in which it is fertilised by insects. Only very small insects are able to penetrate the flowers. The space being very limited these minute insects can enter the flower only in a particular way, and at one of the corners. This causes the pollinia to become attached always to the same place, which is on the outer side of one of the two front legs. When the insect, the carrier of the pollinia, enters a second flower, it can scarcely fail to fertilise the stigma, which is on the corresponding side. Darwin said that it would be difficult to find a case in which there was so marvellously complete an adaptation to a very peculiar mode of fertilisation as the little flower of Herminium. In addition to orchids, there are other flowers the *Darwin, loc. cit. p. 179. † Ibid. pp. 207-208. organisation of which is adapted in a remarkable way to FIG. 2.-Herminium monorchis (after Sowerby, "English Botany," ix. 1869) fertilisation by insects. But to find perfect harmony in the nature of living beings it is not necessary to confine our observations to flowers. The animal world furnishes us with numerous examples. To avoid going into the details of these, I shall content myself with a description of the most remarkable instances. Every one has seen, flying near the ground, small, slender, and pretty wasps. From time to time these bury themselves in the earth or sand, and re-appear in a few minutes. These are the fossorial wasps, the interesting habits of which have been studied by Mr. J. H. Fabre, of Avignon. They are not gregarious, but lead solitary lives and differ in their habits from their congeners. Bees feed their larvæ with honey and pollen which they take to them during the whole period of their development. Wasps are carnivorous, predatory insects, and bring their spoils to their brood of soft and feeble larvæ which are unable to provide for themselves. Bees and most wasps look after the welfare of their young ones in the fashion of human parents in nurseries. Fossorial wasps act differently; they never see their young. They lay their eggs in burrows, sunk in the soil and hermetically sealed. The larvæ are hatched underground and are never seen by the mother. Provision sufficient for their development, however, is made in advance. Before depositing eggs, the females sink the burrows, and fill them with the spoils of the chase, which consist sometimes of spiders and sometimes of crickets or other insects. Each species of fossorial wasps preys on a particular kind of insect or on its allies. for the purpose of provisioning the burrows. These wasps are most fastidious in the choice of their food, and behave like collectors whose interest is only in a single or a few species of small animals. Léon Dufour, the well-known entomologist, was much struck by the ability displayed by certain wasps |