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Grassi has also observed it in Apis, and regards it as the germ of a first, but deciduous, pair of jaws. In the embryo of Hylotoma Graber (Figs. 134, 135) found what he calls three pairs of “preantennal projections,” one of which he thinks corresponds to the “inner antennæ” of Bütschli. This subject needs further investigation.

It thus appears that the procephalic lobes of the embryo of insects, with the rudiments of the antennæ, constitute the primitive head, and perhaps correspond to the annelidan head, while gradually the antennal appendages were in the phylogenetic development of the class fused with the two segments of the primary head. That the second maxillary segment, the occiput, was the last to be added, and at first somewhat corresponded in position to the poison-fangs of centipedes (Chilopods), is shown by our observations on the embryology of Æschna (Fig. 36).

Fig. 36.—Æschna nearly ready to hatch: 4, labium, between T and e the occipital tergite; 5–7, legs.

Fig. 37.—Head of embryo Nematus, showing the labial segment: occ, forming the occiput; cl, clypeus; lb, labrum; md, mandible; mdm, muscle of same; mx, maxilla; mx′, second maxilla (labium); oe, œsophagus.