44 ILLINOIS BIOLOGICAL MONOGRAPHS [44 



As the head is not a single metamere we can not homologize these setae 

 with those of the body segments. 



The ocelli seem to form one of the most satisfactory characters for 

 the separation of genera. In most families their arrangement and the 

 position of the setae associated with them are constant in long series of 

 individuals and species. Without their aid the difficulties in the classifi- 

 cation of some of the Microlepidoptera would be almost insurmountable. 

 The dorsal four usually form the quadrant of a circle, with the other 

 two below them and farther apart. (Figs. 70, 71.) Beginning at the 

 caudal ocellus of the dorsal group we may call them the first to the 

 fourth in regular order. The fifth is caudoventrad of the fourth and 

 in some cases farther ventrad than the sixth (Fig. 77) which is the one 

 most cephalic in position. 



Armature of the body. — In Part One it was shown that lepidopter- 

 ous larvae have certain setae in a definite arrangement. These were 

 denominated by Greek letters and their homotypy was studied in order 

 that any particular letter might be made to apply to the same or homo- 

 typic setae on every segment of every caterpillar. For that study it 

 was necessary to distinguish between primary and subprimary setae, the 

 latter being missing from the first instar. In classification, however, 

 this distinction is rarely of any value, and as subprimaries are few in 

 number the normal ones are assumed to be present in all mature larvae. 

 A statement in a description that a mature larva bears primary setae 

 only, is to be interpreted on this basis. 



The more conspicuous forms of armature are usually associated 

 with groups of setae. "Tubercles", "warts", and "spines" are terms 

 now in use describing them. The first has the disadvantage of meaning 

 any cuticular projection of the body wall from a minute papilla to a 

 conspicuous prominence. "Spines" have also been used both for the 

 projections of the body wall and for the branches of any thorn-like 

 process. A number of new terms are therefore suggested for particular 

 kinds of armature. Their derivation is given except where it will be 

 perfectly evident. 



In the most generalized larvae a seta is surrounded at the base by 

 a small chitinized ring, very slightly raised. This ring may be called a 

 papilla, following Scudder. It is often surrounded by a small and defi- 

 nitely bounded chitinized area or pinaculum (L. pinax, dim., "a small 

 plate"), such as is seen in many Microlepidoptera (Figs. 15, 40). When 

 the pinaculum is conspicuously elevated at the center and bears the seta 

 on a distinct projection, it may be termed a chalaza (Gr. ^a/.a!^a^ 

 "pimple", or "tubercle"), as in the arctian Utetheisa (Fig. 90). 

 Either the pinaculum or the chalaza may be double or triple, and may 



