THE COSTAL FOLD AND DISCAL STREAK. 1639 



The chrysalis is elongated and cylindrifal, but is insuffieiently known. 

 It is said to be thrown into the most violent contortions on the least dis- 

 turbance and often to bend itself so as to make the front part of the body 

 vertical. 



EXCURSUS LXVII.—THE COSTAL FOLD AND DISCAL 

 STREAK OF SKIPPERS. 



Yet let me flap this bug with gilded wings. 



Pope. 



Hardly any special structures in our butterflies are more interesting 

 than those which are peculiar to the male sex and probably serve as 

 odoriferous chambers, though in some instances, where conspicuous, they 

 may also serve as ornamental attractions. 



In no family of butterflies are these more common than in the skippers, 

 where the two tribes known in our fauna are almost always separable by 

 the general nature of these presumably odoriferous chambers, one tribe, 

 the Hesperidi, effectually secreting their androconia in the reflexed margin 

 of the costa of the fore wings, the other, the Pamphilidi, making a con- 

 spicuous feature of theirs in the discal stigma of the upper surface of the 

 same wings. 



The costal fold of the Hesperidi (represented on pi. 45, figs. 2, 3) has 

 been studied by Fritz Midler and by Aurivillius and is reallv a most re- 

 markable structure ; remarkable chiefly because here and only here in 

 butterflies the marginal vein is developed to any appreciable degree ; here 

 it is as highly developed as any other vein, and the membrane between it 

 and the costal vein being exceptionally broad it folds back upon the upper 

 surface so as to lie next the costal vein ; so that though the marginal vein 

 is developed it does not practically form the margin, but, as in the female, 

 that function is given to the membrane in front of the costal vein, here 

 doubled upon itself. The purpose of this reflexion of the costal margin is 

 to form an enclosure within which may be concealed the androconia, 

 probably scent scales, whose odor is probably so delicate that it needs to 

 be bottled up, as it were, within this concealment ; and indeed the closure of 

 the fold is so admirable that it is often diflScult to tell whether or not there 

 be a fold. Within this fold are several distinct sorts of scales, each having 

 its own special field, and these are in general the same throughout the 

 group ; that is, each separate pavement or area bears its own peculiar 

 scales which, though they vary to a considerable degree, even in species of 

 the same genus, are nevertheless generally reducible to a single type, dis- 

 tinct from the others. 



As regards concealment the sexual discal streak of the Pamphilidi is 



