162 



Dr. T. A. Chapman on the 



the zone rises above the floor of the cavity. My observa- 

 tions are, of course, meagre, and this opinion can only go 

 for what it may be worth. 



The same proviso probably applies, though not quite as 

 strongly, as the observations are more definite in char- 

 acter, to my statement that the reverse condition, found 

 in the Plebeiid Blues, does not occur elsewhere. 



If we follow the surface from the genital hollow to the 

 interior of the ductus (azygos, Sharp) we first reach the 

 opening of the membranous sheath ; continuing down this, 

 we reach the zone; here the membrane of the sheath 

 becomes attached to the external surface of the aedeagus, 

 and seems clearly to be an addition to it — that is, the 



Fig. 4. — Suggests that the aedeagus might be advanced by the 

 eversion of the membranous sheath ; this does not, apparently, 

 in fact, ever occur. 



aedeagus here becomes suddenly thicker and denser, and 

 the membranous sheath has all the appearance in most 

 cases of being the outer layer of this portion of the aedeagus 

 set free from the inner; a little further on, however, they 

 seem to be completely fused. Following them on, assuming 

 however, that we are following the outer layer, we arrive 

 at the internal opening of the aedeagus, where the one 

 layer is reflected into the other ; and now returning on our 

 journey, but following the inner layer, we arrive again at 

 the zone and pass on to the free external portion of the 

 aedeagus, and reaching its extremity, return down its 

 interior, along the ductus proper, in which there is no 

 definite line of demarcation between the eversible portion 



