. Smithsonian miscellaneous collections. gs. The prothoracic tergum (fig. 4, Ti) always lacks an antecosta, andthe principal longitudinal muscles (DMcl) that extend forward from 6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 82 the anterior phragma of the mesotergum (iPh) run continuouslythrough the prothorax and the neck (Cv) to be inserted on the post-occipital ridge of the head (PoR). This ridge, as the writer has else-where contended (1928), is evidently the intersegmental fold betweenthe first and second maxillary segments. The neck, therefore, must bederived from the posterior part of the
. Smithsonian miscellaneous collections. gs. The prothoracic tergum (fig. 4, Ti) always lacks an antecosta, andthe principal longitudinal muscles (DMcl) that extend forward from 6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 82 the anterior phragma of the mesotergum (iPh) run continuouslythrough the prothorax and the neck (Cv) to be inserted on the post-occipital ridge of the head (PoR). This ridge, as the writer has else-where contended (1928), is evidently the intersegmental fold betweenthe first and second maxillary segments. The neck, therefore, must bederived from the posterior part of the second maxillary, or labial,segment and from the anterior part of the prothorax, there being nosatisfactory evidence of the existence of a separate neck so, the first postcephalic intersegmental line, or that between thelabial and prothoracic segments (fig. 4, ilsg), must be contained in themembranized cervical region, where the protergal costa is lost. By thesuppression of the primary intersegmental line between the head and. VMcl Fig. 3.—Diagram of the body segmentation of an insect, and the primitiverelation of the longitudinal muscles to the definitive segmental plates of the bodyand to the head; show^ing the reversed overlapping of the sterna betvi^een thethoracic and abdominal regions. Cv, cervix; DMcl, dorsal longitudinal muscles; H, head; IS, first abdominalsternum; IT, first abdominal tergum; Ppt, periproct, or terminal segment;5i, S2, Sz, thoracic sterna; Ti, T2, Tz, thoracic terga; VMcl, ventral longitudinalmuscles; XI, eleventh abdominal segment. the thorax, giving continuity to the muscle fibers of two segments,the head acquires a much greater freedom of motion than it couldhave if it were attached to the body by an ordinary intersegmentalmembranous ring. The loss of the protergal antecosta deprives the prothorax of thepossibility of being a wing-moving segment, and there is nothing tosuggest that the prothorax ever possessed movable organs of
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