182 ANATOMY. 



been considered as exterior sexual organs and sexual apertures at the 

 base of the abdomen in the male Libellula are by no means such parts, 

 as we shall have an opportunity of proving below ; in them also that 

 aperture is found at the end of the abdomen, in the vicinity of the 



anus. 



These vesicular and tubular organs consist, like the intestinal canal, 

 of several divisions, which, as the general character and function of the 

 sexual organs consist in the secretion of fluids, may be distinguished 

 as proper secreting organs (testes and ovaria), conducting organs for 

 the secreted fluids (vasa deferentia and oviductus), repositories for the 

 secreted fluids (vesica seminalis and uterus), and as evacuating organs 

 of the secreted material (ductus ejaculatorius and vagina). These main 

 divisions are found in function, although frequently but little distin- 

 guished in form and figure from each other, in all the internal sexual 

 organs, as will be shown in the course of our investigation. This 

 sketch consequently comprises the most general structure of these 

 organs, and it will therefore be merely the individual, generic, family, 

 and ordinal differences which will occupy us in the course of our inves- 

 tigation ; but we will previously say something about their anatomical 

 structure. 



132. 



The determination of the structural relations of the membranes of the 

 sexual organs is subject to many difficulties, in consequence of the 

 delicacy and minuteness of these parts- It is only in those divisions 

 which possess a greater extension that it has been possible to distin- 

 guish the presence of two layers of membrane. The exterior of these 

 two membranes is coarser, firmer, and of a muscular consistency ; the 

 internal one, on the contrary, is more delicate, transparent, simple, and 

 corresponds with the internal mucous tunic of the intestinal canal or 

 the exterior epidermis. The presence of both the membranes in the 

 large vesicles is subject to no doubt ; they can there be readily and 

 securely exhibited ; even in the more delicate evacuating ducts of the 

 secerning organs they are distinguished by the difference of their con- 

 sistence, which in the internal one is considerably less than in the 

 external one. It is more difficult to prove their presence in the secerning 

 organs themselves, but J. Miiller * has shown them, at least in the 



* Nova Act* Phys. Med. XII. 2. PL LV. 



