Except for its aquatic adaptations, however, the ephemerid °larva is wonderfully thysanuran in character, and possesses conspicuous and distinct maxillulae.
Although the brain is relatively larger, the bones of the limbs, especially the short, five-toed feet, approximate to those of the Amblypoda and Proboscidea; but in the articulation of the astragalus with both the navicular and cuboid Arsinoitherium is nearer the former than the latter group. It is probable, however, that these resemblances are mainly due to parallelism in development, and are in all three cases adaptations necessary to support the enormous weight of the body.
Such adaptations are the transparency and colourlessness of the tissues, and the modifications of the foot, which still shows in Atlanta the form common in Pectin:branchia (compare fig.
He especially pointed out the laws of the " extinction of the specialized " and " survival of the non-specialized " forms of life, and challenged Darwin's principle of selection as an explanation of the origin of adaptations by saying that the " survival of the fittest " does not explain the " origin of the fittest."
Such adaptations are well seen in the leaf of the holly (Ilex aquifolium).