iQio] A Structural Study of Some Caterpillars 107 



represented by the Geometridae, seems to be geologically past 

 its prime. 



On the other hand the group typified by the Noctuidae is the 

 dominant modern type of moths. Though they are much more 

 uniform in adult sti-ucture, there is a vast number of species, and 

 a surprising variety of larval types. In these families the outer 

 side of the leg-base never has more than the three typical setae 

 of vii unless tufted hair is present. There is never but one 

 length of hooks on the prolegs; the front is usually somewhat 

 larger in proportion. Secondary hair is very rare, occurring only 

 in Thaumetopoea, Panthea and Apatela, and only in some 

 species of the latter. A decided majority of the species live on 

 low plants. 



Group I. {with vib, and usually with secondary hair). 



This group again can be divided for convenience into two sec- 

 tions, those with and those without secondary hair. The first 

 includes the Sphingidae, Saturniidae, Bombycidae, Lasiocampi- 

 ■dae and related families: the second, the Notodontidae, Thya- 

 tiridae, Drepanidae, Geometridae, and Lacosomidae, doubtless 

 also the Epiplemidae and Dioptidae. 



The Notodontidae have been an especially puzzling group. 

 Apatelodes shows no distinct affinity to the others, but is in every 

 traceable way more like the Bombycidae and Saturniidae. In 

 hairiness it surpasses both, and approaches the Lasiocampidae. 

 The single-haired Notodontidae (such as Cerura and Hetero- 

 €ampa) show seta vib unmistakably. Datana has secondary 

 hair on the body, and in Melalopha it has invaded the head and 

 the tubercles, producing a kind of tufted hair in which the pri- 

 maries still remain dominant. The distribution of hair on the 

 head is quite difi^erent from that of Apatelodes, with which the 

 moth has been associated. In most ways it would seem 

 more natural to derive the series from the Thyatiridae, and con- 

 sider such genera as Gluphisia and Nadata, primitive. Still the 

 hairy prolegs of Gluphisia* and Nadata would point toward an 

 origin from the series with secondary hair. In the latter case 

 the primitive Notodontan must have had very nearly the structure 

 of Melalopha, with a recessive tendency to have a seta vib. 



■ Lacosoma is a synthetic form between the rest of the series 

 and the Microlepidoptera, with positive relations to both, as 

 will be discussed under the heading of its family. 



* See Packard's figure. Monog. Bombyc. I. PI. Fig. 



