n of man
and the digitate mammals, and yet what differences between their
attitudes when standing! The same holds true as regards the normal
attitudes of the pleuronectids and the other fishes" (p. 107).

The exact way in which Geoffroy homologised the parts of the appendages
in Arthropods with the paired pieces of the typical vertebra is best
shown by the reproduction of his figure of an abdominal segment of the
lobster (Fig. 3), in which the parts homologous with those represented
in the figure of the typical vertebra (Fig. 2) are indicated by the same
letters. The ingenuity of the comparison is astonishing.

[Illustration: FIG. 3.--Abdominal Segment of the Lobster. (After
Geoffroy.)]

The comparison of the Arthropod with the Vertebrate is extended also to
the internal organs. The internal organs of the Arthropod are shown to
stand in the same order to one another as in the Vertebrate, only the
organs are inverted. Thus the nervous system is dorsal in the
Vertebrate, ventral in the Arthropod. Turn the Arthropod on its back and
the relative positions of the systems of organs are the same as in the
Vertebrate. The relation of the organs to the external tube is of course
different in Arthropods and Vertebrates, but this is no contradiction of
the principle of connections. "Such a tube, although it is the organs
essential to life that it contains, can yet behave in different ways
with regard to the mass of these organs: the principle of connections
demands only that all the organs maintain with one another fixed and
definite relations; but the principle would be in no way invalidated if
the whole mass had rotated inside the tube" (p. 112).

Geoffroy pushed the analogy between Arthropods and Vertebrates very far,
for he asserted that every piece in the skeleton of an insect was
homologous with some bone in Vertebrates, that it stood always in its
proper place, and remained faithful to at least one of its
connections.[93] It does not appear that he attempted to prove in detail
this very big assumption, but the beginnings of a detailed comparison
are found in the paper of 1820, _Sur l'organisation des insectes_. Six
segments are distinguished in an insect--the head, the three divisions
of the thorax, the abdomen, and the terminal segment of the abdomen (p.
455).

The skeleton of the insect's head is said to correspond to the bones of
the face, to the bones of the cerebrum and to the hyoid of higher
Vertebrates, the ske