CREATION BY EVOLUTION
nurses use as weaving-shuttles. Throughout the East Indies, Northern AustraHa, India, and equatorial Africa the “tree ants” of the genus Oecophylla (Fig. 7) have attained great proficiency in the art of thus using their larvae for spinning adjacent leaves together (Fig. 8). A similar habit has also been acquired by certain species belonging to two other genera, Polyrhachis, in the tropics of the Old World, and Camponotus, in central and northern South America. The nests made by C. senex and C. formiciformis in the forests of British Guiana, Panama, and Guatemala are extraordinarily like those made by Oecophylla longinoda in the forests of the Congo and by Oecophylla smaragdina in the jungles of India. The structure as well as the behaviour of remotely related species of ants has been similarly modified by convergent or parallel evolution in response to identical environment. A fine example is furnished by certain ants in which the head is cylindrical, constructed like the cork of a bottle, with a hard, roughened, truncated anterior surface, and used for closing the circular orifice of the nest, which leads to galleries excavated in sound wood or in hard soil. Species of at least four different genera in different parts of the world (Camponotus, Pheidole, Crematogaster, and Epopostruma) exhibit this identical form of head. A similar modification of the head is seen in a number of worms, bees, beetles, toads, and tree-frogs; and in certain spiders, beetles, caterpillars, snakes, and armadillos the posterior end of the body is similarly modified for use as a barricade for closing the burrows in which they live and thus preventing the entrance of enemies.
A different modification is seen in certain ants that live in the narrow pith-cavities of the twigs and smaller branches of tropical shrubs and trees. In these insects the whole body becomes very long and slender, or even thread-like, or
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