It will be seen further on that the resemblance is not confined to one species of animal to another species of animal, and one species of plant to a plant of quite a distinct species, but that it also exists between animals and plants. Mr. A. R. Wallace, who, by his most patient and skilful researches in the domain of animal life, has clearly defined and limited the term mimicry as applied in biology, says: “A certain species of plant or animal possesses some special means of defence from its enemies, such as a sting, a powerful and disagreeable odor, a nauseous taste, or a hard integument or covering. Some other species, inhabiting the same district or part of it, and not itself provided with the same means of defence, closely resembles the first species in all external points of form and color, though often very different in structure and unrelated in the biological order.” In South America there are certain butterflies, the Heliconidæ, which are remarkable for the variety and beauty of their colors; but they are incapable of rapid and sustained flight, and would for this reason fall an easy prey to insect-eating birds. Their wings, however, are never found among those rejected by insectivorous birds--in places where the remains of other butterflies frequently cover the ground. The Heliconidæ possess a powerfully disagreeable and pungent odor, which is so little volatile as to cling to the fingers for several days after handling one of these insects. Mr. Wallace inferred from this that they have a disagreeable taste, and would not on that account be eaten by birds. This was subsequently found by Mr. Belt to be the case. Belonging to the family of the Pieridæ, which is quite distinct from the family of the Heliconidæ, and the greater number of which are white, there is a genus of small butterfly named Leptalis, which is eaten by birds. Some species of the genus Leptalis are white, like their allies among the Pieridæ, but the majority of the Leptales have an exact resemblance to some species of the Heliconidæ as far as regards the peculiar shape and color of their wings. The structure of the two families is completely different; in spite of this the resemblance is so strikingly close that both the experienced entomologists Mr. Bates and Mr. Wallace often at the time of capture mistook the one for the other, and only discovered their mistake by a closer examination. This has been looked upon as the most typical example of true mimicry, and is interesting from the fact that it is the first instance to which the term mimicry was applied. It is necessary to distinguish carefully between true mimicry and several similar though superficial modes of resemblance which occur among organic beings. Several orchids resemble flies or spiders, but this is merely a case of accidental resemblance. Among animals of a higher order than insects mimicry very seldom occurs.