VI EXTERNAL STRUCTURE 307 



of Micropteryx (Fig. 211) has however been recently shovs^n to 

 be similar to that of Trichoptera, so that unless it should be 

 decided to transfer Micropteryx to Trichoptera, and tlaeu define 

 Lepidoptera and Trichoptera as distinguished by the condition of 

 tlie pupa, it would appear to be very diificult to retain tlie two 

 groups as distinct. 



Structure of Imago. — Tire head of a Lepidopteron is in large 

 part made Tip of the compound eyes ; in addition to these it 

 frequently bears at the top a pair of small, simple eyes so much 

 concealed by the scales as to cause us to wonder if seeing 

 be carried on by them. The larger part of the front of the 

 head is formed by the clypeus, which is separated by a well- 



FlG. 158.— External structure of a female butterfly, Anosia plexippns. (After Scudder.) 

 a, Base of antenna ; b, pionotum ; 6^, scu4um of mesotliorax ; c, clypeus ; ex, coxa ; 

 d, scutellura ; rf\ soutelluni of metathorax ; e, post-scutellum ( = base of phragma) ; 

 em, epimeron ; «?), episternuni ; /, scutum of metathorax ; m, basal part of pro- 

 boscis ( = maxilla) ; 0, eye ; p, labial palp ; r, mesosternum ; s, prothoracic 

 spiracle ; t, tegula ; tr, trochanter ; 1-9, dorsal plates of abdomen. 



marked line from the epicranium, the antennae being inserted 

 on the latter near its point of junction with the former. There 

 is sometimes {Saturnia, Castnia) on each side of the clypeus a 

 deep pocket projecting into the head-cavity. The other parts of 

 the head are but small. The occipital foramen is very large.^ 



The antennae are always conspicuous, and are very various 

 in form ; they are composed of numerous segments, and in the 

 males of many species attain a very complex structure, especially 

 in Bombyces and Psychidae ; they doubtless function in such 

 cases as sense-organs for the discovery of the female. 



The largest and most important of the mouth-parts are the 

 maxillae and the labial palpi, the other parts being so small as 

 to render their detection difficult. The labrum is a very short, 

 1 Kellogg, Kansas Quarterly, ii. 1893, p. 51, plate II. 



