608 Mr. D. Sharp and Mr. F. Muir on tlu Comparative 



of the types the internal sac is everted during copulation, 

 and it is probable that this method is the usual one ; 

 though the Coram by cidae 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 cliitinisation 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 (i. e. Hyclro2)hilus). 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 Eumolpus and Chrysoclius the stenazygos forms a very 

 long slender structure like a flagellum. 



Bordasf 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, etc. Bordas considers that tliis 

 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. 



t C.R. Ass. franc, av. Sci., 1899, p. 540. 



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