265] NOCTUID LARVAE— RIPLEY 23 



form. Larger groups of genera or even single genera may be often sepa- 

 rated by characters based on the length and form of the spinneret more 

 readily than by any other means. The general type of this organ is usually 

 the same for large groups. Some of the most fundamental and valuable 

 characters for the taxonomic treatment of noctuid larvae are provided by 

 the spinneret. The failure of previous workers to appreciate the phylo- 

 genetic significance of its variations has probably been due to its small size, 

 which often necessitates the removal of the labium to allow careful exami- 

 nation. This operation, however, is performed with the utmost readiness 

 by means of a single stroke of a needle. 



The types of spinneret within the Noctuidae, unlike those of the mandi- 

 bles, can be largely correlated with biological characteristics. The amount 

 of silk employed as a protective covering for the pupa varies extensively 

 according to the situation in which pupation takes place, the type of loca- 

 tion selected being generally characteristic for the taxonomic group. 

 Noctuid larvae usually pupate either within a cocoon or a subterranean 

 cell. The cocoon may be fairly dense, as in many Acronyctinae and 

 Phytometrinae, to very slight, as in the genus Polia of the Hadeninae. It 

 never approaches those of the Saturniidae in density or in the amount of 

 silk em^ployed, being usually very sHght, although often supplemented by 

 foreign matter such as leaves or grass or by setae from the verrucae in 

 Acronycta, where these structures are present. Those which pupate 

 beneath the soil, on the other hand, usually spin but a few threads, as in 

 Cirphis vnipiincta, or no silk whatever, a condition exemplified by most 

 species of Agrotinae which have been reared by the author. 



This reduction in the amount of silk used for a pupal covering is also 

 met with in certain other families, notably in the butterflies, where only a 

 button of silk is spun for the attachment of the cremaster, in the Sphingidae, 

 which usually enter the soil to pupate, spinning little or no silk, and in 

 certain leaf-miners, which, according to Tragardh, have lost this habit in 

 correlation with their protected habitat. The accompaniment of pupation 

 beneath the soil or in similarly protected situations by a marked reduction 

 in the amount of silken covering, appears to be of general if not of universal 

 occurrence. It should be noted, however, that the converse is not true, 

 the naked pupae of butterflies having developed other means of protection 

 than subterranean pupation. 



An interesting instance of individual variation in the amount of silk 

 spun is furnished by four larvae of Polia lorea. Two were taken on the 

 floor of typical Illinois forest, the other two being collected on the following 

 day on the prairie, about six miles from the nearest woodland. The latter 

 were feeding upon sweet clover, the former upon some plant not definitely 

 known, probably Geranium maculalum, but not upon any species of Tri- 

 folium, since none was present in the vicinity. The two larvae of the 



