OF WASHINGTON, VOLUME XVIII, 1916 155 



In studying the head we find that while under different condi- 

 tions of environment it assumes a multitude of different shapes 

 and is variously modified in the proportionate development of 

 its organs and parts, that such changes are frequently more super- 

 ficial than fundamental. Certain characters still persist in their 

 typical form through most of the changes. Even when there is 

 a radical and fundamental alteration in structure due to the same 

 environmental stimulus the forms differ in groups of different 

 origin. The best examples of this are found among the leaf and 

 bark mining larvae that have become adapted to sap-feeding 

 (Comp. Tragardh (8) ). The flat heads of all the Gracelariidae 

 conform to one general family type while those of Phyllocnistis 

 modified in the same organs and to the same purpose, exhibit a 

 quite different form. Among the tissue feeding miners the dif- 

 ferences are also striking. Ectoedemia and Opostega, for example, 

 inhabit flat serpentine mines and have the head similarly de- 

 pressed but differ in fundamental structure. 



The generic and larger group characters of the head are found 

 in the shape and proportions of the head capsules, the character 

 of the frons, the setae and the trophi. Color and color markings 

 are at most of specific importance. Very often they vary in 

 individuals, or in different stages of the same larva. The shape 

 and intensity of pigmentation in the ocellar area is also variable, 

 being often unevenly distributed on opposite sides of the same 

 head. 



HEAD CAPSULE. 



The general shape of the head capsule is a character that must 

 be used with considerable caution. By itself and unsupported by 

 other characters it is worthless in many groups. In certain spe- 

 cialized families and subfamilies it is diagnostic. The rounded, 

 caudally-extended and widely separated blade-like dorsal hind 

 margins of the epicranium are typical of the Nepticulidse. Mne- 

 monica and Dorata have projections resembling these but much 

 longer, differently shaped and closer at the extremities. The 

 horse-shoe shaped head of Tischeria and the wedge-like heads of 

 the flat gracilariids are characteristic. On the other hand, the 

 free-feeding Micros have much the same type of head. There is, 

 for example, little or nothing in the general shape to distinguish ;i 

 gelechiid from a tortricid or a phycid. Taken together with other 

 characters, however, peculiarities of shape are significant and con- 

 stant within a genus. The general shape and proportions of the 

 head capsule should be noted in larval descriptions. In our joint 

 paper (7) on A. xtrnjijinihUn, Fr. Dc( iry.se and the writer have 

 designated the line of greatest width as the norm of comparison 

 in expressing proportions of the head capsule. This is a purely 



