NO. 1310. NORTH AMERICAN lUYSANOPTERA— HINDS. 107 



Stigmata. — Either three or four pairs of stigmata arc present in 

 Thysanoptera, In the adult they appear constantly at the anterior 

 anoles of the mesothorax, and on the sides of the tirst and eighth a})dom- 

 inai segments, while the fourth pair, always present in Tubulif era and 

 sometimes distinguishable in Terebrantia as well, occurs close behind 

 the attachnuMit of the hind wings. Uzel sfeites that four pairs of spi- 

 racles are jjresent in the Terebrantia. This is surely often the case, 

 but the metathoracic pair is very small, and in some species I can not 

 find it even in specially prepared mounts, and in some cases where 

 traces of the stigma can be found, 1 am convinced that it is vestigial 

 and really functionless. The mesothoracic stigma is frequently elon- 

 gated dorso-ventrally, sometimes being very narrow. 



In the larv{\? the stigmata are situated at the front angles of the 

 mesothorax and upon the sides of the second (instead of the first) and 

 eighth abdominal segments. 



The structure of a stigma is peculiar. In a surface view at the 

 sharpest focus, upon an anterior abdominal stigma of, e. g. , Anapho- 

 thrJpx .striatum, cleared in caustic potash, the stigma appears to be 

 made up of a number of irregularly polygonal, cell-like bodies, sep- 

 arated from each other by dark lines and each cell showing one or 

 more dark spots near its center. In focusing down onto its surface, 

 its appearance changes quite strikingly. As it first comes into view, 

 though before it is clearly seen, it appears as a dark field with quite 

 regular, small, light spots, the dark lines giving a reticulate appear- 

 ance. When a little more nearly in focus, the cells appear dark, while 

 the central spots and the intercellular lines and angles are very much 

 lighter. Brought into sharp focus, the cells are seen to be more irreg- 

 ular than they appeared at first, the surface appears light colored, 

 whereas formerly it appeared dark, while the intercellular lines and 

 central spots have now become dark (Plate X, fig. 112.) This reversal 

 of the light and dark parts is peculiar and very noticeable. On one 

 side of the center a larger, rather indistinct, rounded area can usually 

 be seen, which is the bulbous enlargement at the end of the trachea 

 opening by a quite large orifice to the exterior. A cross view of a 

 stigma (Plate X, fig. 113) shows a remarkable structure. The cellular 

 areas are now found to be mushroom-like bodies with slender stalks, 

 standing with their heads close together. These are quite strongly 

 chitinized and dark. ^Vhether the little air chambers between them 

 connect in any way with the trachea has not yet been determined. 



SEXUAL characters: terebrantia. 



Female ovfposUor. — The most prominent external sexual character 

 of the female is the ovipositor which is attached to the ventral side of 

 the eighth and ninth abdominal segments (Plate XI, fig. 121) and is 



