In the most highly developed forms the two anterior divisions (tagmata) of the body, prosoma and mesosoma, each exhibit six pairs of limbs, pediform and plate-like respectively, whilst the metasoma consists of six limbless somites and a post-anal spine.
On the other hand, the two limbless segments that precede the caudal furca are decidedly non-malacostracan.
But the limbs show with regard to development great variation, and an uninterrupted transition from the most perfect condition of two pairs with five separate clawed toes to their total disappearance; yet even limbless lizards retain bony vestiges beneath the skin.
The motions of these limbless lizards are similar to those of snakes, which they resemble in their elongate body.
Presumably the presence of osteoderms and of complete cranial arches are more archaic than their absence, just as we conclude that limbless forms have been evolved from various groups possessed of fully developed limbs.
Some are entirely arboreal, dwellers in forests, while others, like Cnemidophorus and Asneiva, are strictly terrestrial, with great running powers; a few dwell below the surface and are transformed into almost limbless ' For anatomical detail and experiments, see R.
The same applies to the limbless little Ophiopsiseps nasutus of Australia.
Sometimes they are applied, as in the Copepoda, to the limb-bearing and limbless regions of the trunk, while in other cases, as in the Phyllopoda, they denote, respectively, the regions in front of and behind the genital apertures.