608 Mr. D. Sharp and Mr. F. Muir on the Comparative 
of the types the internal sac is everted during copulation, 
and it is probable that this method is the usual one; 
though the Cerambycidae may be peculiar in their mode 
of eversion. 
In a great many forms the line of demarcation between 
the internal sac and the median lobe is obscured, for in 
some cases the chitinisation of the median lobe is continued 
on to the internal sac, and in others the distal end of the 
median lobe is membranous. ‘The fact that in many cases 
the basal portion of the sac, and in other cases the whole 
sac, is permanently evaginated prevents us from distinguish- 
ing the two portions by their positions when at rest.* 
Of the zygotic portion of the genital tube we do not 
speak, as it is beyond the scope of this memoir. And the 
stenazygos only concerns us because in many forms it is 
impossible to sharply define it from the eurazygos, before the 
latter is reflected to form the phallic portion of the tube. 
In such forms we speak of the internal sac being undiffer- 
entiated G.e. Hydrophilus). In cases were the internal 
sac is differentiated it is sharply defined from the stenazy- 
gos by its size, and often by chitinisations situate on the 
sac at the point of juncture of the two parts. 
In Lumolpus and Chrysochus the stenazygos forms a very 
long slender structure like a flagellum. 
Bordast has pointed out the existence of two completely 
separated ejaculatory ducts in certain Longicorns (Lamia, 
Batocera, etc.). We have also observed this fact in some 
Monohammus, Gnoma, ete. Bordas considers that this 
furnishes an argument in favour of the theory that the 
terminal parts of the canal were primitively of paired 
origin. It is possible, however, that this feature is of 
secondary origin, brought about by the abbreviation and 
suppression of the stenazygos and the lengthening of 
the zygotic portions, thus causing the zygotic portions to 
open into the eurazygos; in some Monohammus there is a 
short stenazygos (fig. 221a). 
* Since this was written one of the writers, F. Muir, has observed 
the development of the aedeagus in Sphenophorus obscurus. The 
median lobe and internal sac arise as a single tube which eventually 
differentiates into these two portions, the internal sac not being in- 
vaginated into the median lobe until the pupa is fully developed and 
ready to emerge. In many forms, as we have remarked, no distinct 
line of demarcation ever appears. 
ft C.R. Ass, frane. av. Sci., 1899, p. 540. 
