196 ANATOMY. 



comparison between this organ and that of Locusta, the lower moveable 

 processes are analogous to the two valves of the vagina bivalvis, the 

 superior ones however to the spinous processes contiguous to the anus, 

 but with this difference, that in Locusta these processes are articulated 

 to the horny piece which bears them, and which lies between the 

 orifice of the vagina and the anus ; in Gryllus, on the contrary, the 

 superior processes form an integral portion of that horny piece. Acheta 

 agrees in structure with Locu.sta, but its vagina is more delicately 

 constructed; the anal processes are longer, and at their apex apparently 

 jointed. 



The female Tipula have likewise a bivalve vagina which very much 

 agrees in structure with that of Gryllux. In Ctenopkora alrata, two 

 pointed, long, and sabre-shaped processes originate above from the last 

 dorsal plate, and bend from the sides towards each other, forming a 

 bivalved vagina. They correspond to the superior immoveable processes 

 of Gryllus or the moveable processes of Locusta. Beneath this last 

 dorsal plate, and consequently between the valves, the anus is placed. 

 A triangular fleshy process encompassed by a delicate horny margin 

 separates it from the orifice of the vagina lying beneath it. It also 

 has on each side two processes of the last ventral plate, which are 

 above shorter, broader, inwardly arcuate, and gently bowed externally. 

 These two valves form the true vagina, and therefore correspond to the 

 inferior processes in Gryllus and the long vaginal valves in Locusla. 

 In a state of repose they lie concealed between the superior or anal 

 processes, and all four appear to form a bodkin-shaped process. 



145. 



The TEREBRA, or ACULEUS, is found in all the Hymenoptera and 

 in the Cicadaria. 



With respect to the aculeus of the Hymenoptera, although it has 

 been occasionally tolerably well explained by the earliest entomologists, 

 it has not always been recognised by modern ones, and therefore fre- 

 quently imperfectly described. This fact is the more striking as it 

 has actually nearly the same structure in its essential parts in all the 

 families, and is merely subject to slight differences of form. For the 

 present we will pass these over, and proceed to examine its essential parts. 



The chief character in which the terebra is distinguished from the 

 vagina bivalvis is the presence of a second pointed boring organ lying 

 between the valves. This fuller development of it is not found in the 



