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 well seen in the leaf of the holly (Ilex aquifolium).
For later versions and adaptations of the saga see O.
They are true Pectinibranchia which have taken to a pelagic life, and the peculiarities of structure which they exhibit are strictly adaptations consequent upon their changed mode of life.