ed faithful to the principle of connections, at
least at their points of insertion.[137] Audouin gave the detailed
demonstration of this by his accurate and minute determination of the
pieces of the arthropod skeleton. He recognised that the body of
Arthropods was made up of a series of similar rings, and that even the
compact head of insects consisted of fused segments. In each segment
Audouin distinguished a fixed number of hard chitinous parts, the dorsal
tergum, the ventral sternum, the lateral "flanc" of three pieces, all to
be recognised by their positions relative to one another. Many of the
names which he proposed are still in use; it was he who introduced the
terms prothorax, mesothorax, and metathorax, for the three segments of
the insect's thorax. He used Geoffroy's _Loi de balancement_ to explain
cases of correlative development, such as the relation between the size
of the front wings and the development of the mesothorax. In another
paper Audouin compared the three pieces of the dorsal skeleton of
Trilobites to the tergum and the upper part of the "flanc."[138] In a
third paper of about the same time he tried to establish the homologies
of the segments throughout the Articulate series--with less success than
Savigny.

Later on, in conjunction with Milne-Edwards, he demonstrated the unity
of composition of the nervous system in Crustacea, showing how the
concentrated system of the crab was formed by the same series of ganglia
as in the Macrura.

The entomologist Latreille also tackled the problem of the homologies of
the segments in the different classes of Arthropods (Cuvier, _loc.
cit._, p. cclxxii.). He thought he could find fifteen segments in all
Arthropods. He made the retrograde step of likening the head of insects
to a single segment. But some of his homologies showed morphological
insight, _e.g._, his comparison of the "first jaws" of Arachnids to
antennae, because they were placed above the upper lip. It was he who
first pointed out the resemblance of the leaf-like gills of Ephemerid
larvae to wings, and suggested that wings were "a sort of tracheal feet."

He made also a rather hazy and speculative contribution on Okenian lines
to the problem of the relation of Arthropods to Vertebrates, likening
the carapace of Crustacea to an enormously developed hyoid, the
appendages of the tail to the ventral and anal fins of fish. The
masticatory organs of Arthropods were jaws disjointed at their
symphysi