28 PEOC. ENT. SOC. WASH., VOL. 20, NO. 2, FEB., 1918 



must be remembered that these forms, however primitive they 

 may be in group origin, are all highly specialized representatives 

 upon whom biological influences have produced a startling and 

 wide variety of modifications. What is lost, or retained, or 

 changed is therefore of considerably less significance than how 

 the loss or change came about or how adverse or favorable the 

 biological conditions have been to any character that has been 

 retained. The tendency to lose certain veins rather than others 

 where either could be sacrificed to the same advantage, or the 

 tendency to modify certain parts of the larval head rather than 

 other parts when either modification would produce a form 

 equally suited to conditions is more important than the mere 

 form that results. One is distinctly an inherited character, the 

 other often merely biological. 



This brings .us to our consideration of the larva of Opostega 

 (Plate I) with which we are here chiefly concerned. In general 

 appearance it resembles nothing in the Lepidoptera except in a 

 very superficial way certain sap-feeders of the Gracilariidae 

 with which it has in reality nothing in common. The head 

 (figs. 8, 9) is oval, wedge-shaped, widest near the hind margin, 

 flattened to a extreme degree, with two long, thin blades (Bl) 

 articulated to the dorsal hind margin at the posterior extremities 

 of the adfrontal ridges (ADFR) and extending into the pro- 

 thorax. The frons (FR) is widest at the hind margin, narrow- 

 ing slightly anteriorly and bearing the two frontal punctures 

 (Fa) just back of the anterior margin. The frontal setae are 

 absent as are also the adfrontal areas with their setae. There is 

 nothing to correspond to the bridge (Ob, figs. 16, 33) connecting 

 the posterior dorsal extremities of the adfrontal ridges in so many 

 leaf and bark miners, and so conspicuously developed in the 

 sap-feeding Gracilariidae. The articulation between frons and 

 epistoma is very decided and the latter part greatly developed, 

 fused with pleurostoma (EP + PLR) and completely enclosing 

 all but the anterior margin of the labrum. The labrum (L, 

 fig. 1) itself is very peculiar. It is thin, weakly chitinized, and 

 capable of little or no movement. There is one median and one 

 lateral, hairless tubercle on the anterior margin on either side of 

 the epipharyngeal shield. Both the epipharyngeal teeth (ET) 

 and the epipharyngeal shield (ES) are enormously developed and 

 thrust well forward of the limits of the labrum. The shield 

 might easily be mistaken for the labrum itself save that it bears 

 no setae or punctures and has none of the muscle attachments 

 peculiar to that organ. Of the epicranial setae only three re- 

 main, two on the dorsal surface (representing most probably 

 A-l, and A -3) and one on the ventral surface (one of the larger 

 of the sub-ocellar or ocellar groups, either SO-3 or 0-5) . There are 



