Pairing of the Plebeiid Blue Butterflies. 167 



In most of these cases the ostium and its armature, if any, 

 is all that there is to represent the 8th abdominal seg- 

 ment. Nor, indeed, is there often any chitinous plate to 

 represent either the 9th or the 10th abdominal sternites. 



In all cases (" all " must be understood to mean merely 

 within my observations and experience) in which the 

 ostium is within the margin of the 7th segment, it appears 

 to be the outer end of a chitinous cervical tube (PL XVIII 

 and XIX). 



When there is any armature it appears to fix the ostium 

 more or less just outside the margin of the 7th segment 

 (PL XXI and XXII, fig. 2). 



The peculiarity in the Plebeiids is that the ostium is 

 carried by a small chitinous plate ; but there is a special 

 extensible structure by which this plate may be extruded 

 as far or further than the end of the ovipositor. 



When at rest the plate occupies the usual position of 

 the ostium, viz. at the margin of the 7th segment, but 

 behind it is the apparatus for its projection. 



In PL XXXI the parts are shown as they are when at 

 rest. In PL XLII they are seen partially extruded. In 

 the majority of the figures they are shown fully extruded, 

 or as nearly so as is easily obtainable in making the 

 preparations. 



It is seen that the small terminal plate is carried at the 

 end of a long membranous tube, when this is extended, 

 and the appearance at first sight suggests that the function 

 of the eversible membrane of the aedeagus has somehow 

 been transferred to the female structures. This is, of 

 course, absurd ; its real function is to carry the ostial plate 

 to the fundus of the male genital cavity so that it may 

 meet the very short and immovable aedeagus. A function 

 almost as surprising as the impossible one mentioned, and, 

 so far as I know, without any parallel amongst other 

 Lepidoptera. 



This eversible structure consists of two portions — the 

 outer one, that is often simply membranous, but carrying 

 the terminal plate, and an inner one, that is reversed by 

 invagination when it is retracted, and which is strengthened 

 bv a loop of chitin; this may be seen in the PL XXXI 

 to XLVII. 



I have named these two portions, the inner the " prop " 

 {Iti/postema), and the outer the " rein " (henia). (By a 

 misprint in Trans. City of London Ent. Soc. heina.) 



