OF WASHINGTON, VOLUME XVIII, 1916 137 



noniously with the pushing clown of the spiracular area to form 

 the thoracic alar area, the muscles (t/>-pn) have become strength- 

 ened and retain their same relative position (tp-pn 1 ) but the 

 spiracle has moved below the tergopleural suture as the muscle 

 (*l>i-pn) shows, which moves with it. Thus the spiracle has 

 moved into the pleural region. This muscle is small in the meta- 

 thorax with the rudimentary spiracle, but large in the mesothorax. 

 It is of great importance in deciding the segment to which the 

 spiracle belongs when it has apparently moved from mesothorax 

 to the prothorax, as in some Lamiinae and other larvae. 



The rudiments of the lines defining the spiracular ellipsoid can 

 still be seen in the metathorax (especially the Cerambycinse) 

 but it is debatable whether to consider this region into which the 

 spiracle has moved in the thorax as part of pleurun which it 

 evidently was in the abdomen or to consider this spiracular 

 triangle, as fused with the narrow piece of intersegmental skin 

 and thus a part of it instead of the pleurum. In the mesothorax 

 of Prioninae and Lepturinae this triangle is very sharply defined. 

 For the sake of comparison in larva? of other families the latter 

 view is adopted, for the present, i.e., that the spiracle lies in the 

 intersegmental skin of the pleurum. In another subfamily of 

 cerambycids, Aseminae, the spiracle in the first abdominal seg- 

 ment has moved forward out of the ellipsoid past the line a.*./. 

 (Plate 8) into the intersegmental skin, thus giving more evidence 

 for the latter theory. 



To consider the formation of the notal subdivisions it may bo 

 well to start with the clerid in which form Dr. Boving has shown 

 that the large muscle s-pn (attached very high) and the muscle 

 pscl-hypl behind, cause elliptical constrictions, the prescutum 

 and postscutellum. In the cerambycid it has been shown that 

 the postscutellum is absent. Now from the lowered attach- 

 ment of the muscle s-pn 2 and greater protuberance of the ampullae 

 with its many muscles, the preponderance of stress in this region 

 is determined by the latter, forming curved lines as the limit of 

 the parascutum. Therefore the presternurn cannot take its 

 triangular form. But in the thoracic segments, the muscles 

 s-pn- have pushed their upper attachment dorsad and by the 

 loss of the large muscles sc-pn a poorly developed ampulla results 

 with the consequential forming of a triangular prescutum and 

 scutellum. Whether new sutures are formed in the thorax or 

 the old ones modified is questionable, probably either alternative 

 occurs in different forms of larvae. It is assumed as the muscles 

 seem to indicate that the anterior and posterior sutures defining 

 abdominal scutum a.sc and p.sc., have fused medianly and diverged 

 laterally, thus opening scutum which fuses with parascutum to 

 form what is collectively called in the thorax, scutum (Sc). 



