Dr. T. A. Chapman on Plebeiid Blue Butterflies. 157 



list, six are Plebeiids, and of the other five, two, argiades 

 and boelica, can hardly be called natives. Of European 

 species there are nearly three Plebeiids to two of other 

 tribes, and the same is about the ratio in the whole Palae- 

 arctic area. So far as my knowledge extends, no Plebeiidi 

 are found south of the Palaearctic (and Nearctic) region, 

 except the genus Chilades, a genus less typical of the tribe 

 than any other. This is quite subtropical, if not tropical, 

 in its distribution; (Potyommatusl) martini and allardii, 

 occurring in Algeria though not in Europe, seem to be 

 the most southern of typical species, but are always 

 tabulated as Palaearctic. 



I have no systematic objects, but shall for convenience 

 adopt the genera given in Tutt's " British Lepidoptera." 



The male appendages of the Plebeiids are remarkably 

 similar throughout the tribe, both in the form and 

 character of the clasps and of the dorsal armature, and 

 differ very much from those of other "blues" in these 

 structures. These are so frequently figured in papers of 

 my own in our Transactions, in Tutt's " British Lepidop- 

 tera" and elsewhere, and by others, that I need not dilate 

 on them. 



Before describing the actual structural peculiarities of 

 the Plebeiids, that bear most directly on the subject of 

 this paper, it may be useful, as some basis of comparison, 

 to say a few words as to what, so far as my meagre know- 

 ledge permits, is the most usual structure of these parts 

 that obtains in other Lepidoptera, or rather to indicate 

 something of the range of variation that obtains in those 

 portions of the appendages that in the Plebeiids are at the 

 extremity of the range in a certain direction. 



The most characteristically specialised of these in the 

 Plebeiids is the penis, which has to reach the bursa and 

 provide it with the product of the male glands. 



The penis consists usually of two portions — the aedeagus, 

 a solid, basal, highly chitinised portion, and the eversible 

 membrane (vesica, Pierce); the latter often armed with 

 spines, etc. (cuneus, Stitz, cornuti, Pierce). 



When pairing takes place the bursa copulatrix is reached 

 either by the aedeagus, or by the extension of it constituting 

 the eversible membrane. 



A conclusion one early arrives at in examining these 

 structures is that the aedeagus and the eversible membrane 

 are continuous portions of one structure (or tube), as is, 



