Chapter II: APODA (15).--No limbs. Tail vestigial or absent. Frontal bones

distinct from parietals; palatines fused with maxillaries. Male with
an intromittent copulatory organ. Degraded, worm-like batrachians of
still obscure affinities, inhabiting tropical Africa, south-eastern
Asia and tropical America. Thirty-three species are known. No fossils
have yet been discovered. It has been attempted of late to do away
with this order altogether and to make the Caecilians merely a family
of the Urodeles. This view has originated out of the very remarkable
superficial resemblance between the _Ichthyophis_-larva and the
_Amphiuma_. Cope (16) regarded the Apoda as the extremes of a line of
degeneration from the Salamanders, with _Amphiuma_ as one of the
annectent forms. In the opinion of P. and F. Sarasin (17), whose great
work on the development of _Ichthyophis_ is one of the most important
recent contributions to our knowledge of the batrachians, _Amphiuma_
is a sort of neotenic Caecilian, a larval form become sexually mature
while retaining the branchial respiration. If the absence of limbs and
the reduction of the tail were the only characteristic of the group,
there would be, of course, no objection to unite the Caecilians with
the Urodeles; but, to say nothing of the scales, present in many
genera of Apodals and absent in all Caudates, which have been shown by
H. Credner to be identical in structure with those of Stegocephalians,
the Caecilian skull presents features which are not shared by any of
the tailed batrachians. G.M. Winslow (18), who has made a study of the
chondrocranium of _Ichthyophis_, concludes that its condition could
not have been derived from a Urodele form, but points to some more
primitive ancestor. That this ancestor was nearly related to, if not
one of, the Stegocephalians, future discovery will in all probability
show.