158 



Dr. T. A. Chapman on the 



of course, obvious when the membrane is everted; but 

 beyond this, that the external portion of the aedeagus 

 only differs from the membrane by being chitinised, and 

 that the length of the external portion of the aedeagus 

 varying in different species, and often greatly in closely 



Fig. 1. — Diagram of aedeagus (founded on Thecla) when retracted. 



Fig. 2. — Diagram of aedeagus when exserted. 



Fig. 3. — Similar diagrams of aedeagus in an Erebia. The lettering 

 indicates : — 



A. Chitinous tube of the aedeagus, external portion. 



O. The opening in the floor of the genital cavity, through 

 which the aedeagus is advanced and retracted. 



S. Membranous sheath, sinus (Kusnezov), derived from floor 

 of cavity, that permits this movement, stretched in fig. 1 

 during retraction, gathered together in fig. 2. 



Z. The zone at which 8 is attached to the aedeagus. 



B. Internal portion of aedeagus continuous with A, but 

 having an outer layer continuous with S. 



E. Internal opening of aedeagus, where the two layers are 



reflected into each other. 

 D. Ductus ejaculalorius, continuing upwards into A, and 



reflected from it at its free margin, i. e. continuous with it, 



forming in this region the eversible membrane (vesica, 



Pierce) armed with C (cuneus, cornvti). 

 The same explanations apply to fig. 3, which gives advanced 



and retracted positions of the aedeagus. 



allied species, does not depend altogether on a greater or 

 less development of a special portion of the aedeagus, viz. 

 that beyond the zone, but in the greater or less extent of 

 the azygos (Sharp) tube that is chitinised to become 

 aedeagus or remains membranous as eversible membrane. 



