269] NOCTUID LARVAE— RIPLEY 27 



SETAE OF TRUNK 



A number of the earlier students of lepidopterous larvae noted the 

 definite arrangement of certain setae throughout large groups, which led 

 them to investigate the taxonomic value of setal position. IMiiller in 1S86 

 and Dj-ar in 1894 published important works on this subject, the latter 

 attempting to make a table to the families of Lepidoptera based on the 

 setal pattern of the larvae. The distinction between primary and secondary- 

 setae was recognized by Miiller, Dyar subsequently introducing the term 

 subprimary, which he applied to setae of general occurrence which are 

 absent from the first instar. The most extensive researches on the setae 

 of the trunk have been performed recently by Fracker in 1914 and by 

 Schierbeek in 1917. The former author has provided us with a most useful 

 and easily workable table for the identification of caterpillars, exclusive of 

 the Noctuidae, in which work the setae play an important part. The latter 

 investigator pursued the subject from the morphological point of view 

 . rather than from the systematic one. These two workers disagree on the 

 selection of a primitive type of setal position, Fracker regarding the pro- 

 thorax as presenting the more generalized position, while Schierbeek gives 

 good reasons for considering the abdominal segments which bear larvapods 

 as the more primitive. They hold different views, moreover, as to the 

 homodynamies between thoracic and abdominal setae. On at least one 

 important point they agree, namely, that verrucae correspond to single 

 primary setae, the former having been developed from the latter, and, in 

 certain groups, having been subsequently reduced again to single setae, 

 this process being a reversible one. 



Inasmuch as an investigation purposing to settle the disagreements of 

 these two workers would involve a detailed study of the larvae of the whole 

 order, the disputed questions of homodynamy and primitive segments 

 cannot be decided from researches on the Noctuidae alone. It is conse- 

 quently not a part of the plan of this work to discuss these points. The 

 treatment of the setae of the trunk here presented will be confined chiefly 

 to a discussion of the variation in the setal pattern of noctuid larvae, 

 exclusive of those which bear verrucae, as in Acronycta. The forms with 

 tufts of setae are confined within the family to this genus and to a few 

 allied ones of little importance. Since they present various stages in the 

 development and reduction of verrucae, these genera promise a rich field 

 for the study of the evolution of setal tufts. 



Of the various systems of naming setae which have been proposed that 

 of Fracker is undoubtedly the most satisfactory. As Schierbeek states, the 

 older system of numbering them has resulted in so much confusion that any 

 further schemes employing numerals would only increase our diiSculties. 

 He rejects Fracker's Greek letter system, apparently because he disagrees 

 with the homodynamies proposed by this author, and proceeds to apply 



