362 Annals Entomological Society of America [Vol. XII, 



there are merely hairs or weak functionless setae on the frenulum- 

 bearing area ; in these the function of holding the wings together 

 is performed by some other structure. In the males of some of 

 these, viz., Nepticulidae, Prodoxus, Adela, etc., there is a strong 

 single-spined frenulum, formed by the fusion of several spines, 

 in some instances of as highly specialized a character as is 

 found in any Lepidoptera. These forms furnish no evidence 

 of the phylogenetic process of development of the frenulum or 

 frenulum hook, but such evidence is furnished by the condition 

 of the frenulum in some members of several groups which 

 conserve other primitive characters. In Cossidae and Megalo- 

 pygidas the frenulum is in a rudimentary condition, consisting 

 of a bunch of spines, and in the females of many moths it con- 

 sists of two or several spines. Of the process of transition 

 from more primitive modes of holding the wings together to a 

 functional frenulum, we have very little evidence. In this 

 connection, the condition found in Promiba is significant. In 

 the female Pronuba yuccasella all except the two most proximal 

 of the row of costal spines have become flattened and scale-like, 

 and these- two remaining spines are larger than any of the 

 corresponding series found in Prodoxus, which is an allied, 

 though more generalized genus. In addition in the female 

 Pronuba the beginnings of a true frenulum are shown, con- 

 sisting of a tuft of short, weak spines at the distal end of the 

 costal sclerite in the same position as the frenulum of the male. 

 There is also an inwardly projecting row of scales from the 

 costa of the fore wing, apparently the beginning of a frenulum 

 hook, which is present in the male. The female frenulum is 

 not long enough to reach this row of scales, which is, however, 

 easily reached by the two strong costal spines, which may thus 

 function as a frenulum before the true frenulum has reached 

 a sufficient size to be functional. These two spines are not 

 present in the male Pronuba, which has a single-spined frenu- 

 lum. In the Nepticulidae there is no stage in the development 

 of the frenulum intermediate between the minute functionless 

 spines of the female, and the strong single-spined frenulum of 

 the male. However, the fact that functional costal spines and 

 frenulum are occasionally present at the same time, indicates 

 that the costal spines retain their function up to the time that 

 it is taken over by the frenulum. In the Cossid, Prionoxystus 

 robinice, where the frenulum is rudimentary in both sexes, the 



