THE EXTERNAL GENERATIVE ORGANS. 733 



in the form of hooks and scales. In many male Insects they 

 have been described as the external sheath of the penis. 



The Posterior Gonapophyses. These appear in the embryo in 

 the Orthoptera and Hymenoptera as the external pair of 

 papillae on the posterior border of the mesogenital somite, 

 usually the ninth abdominal somite. They are the superior 

 blades of the ovipositor in the female of the Orthoptera, and 

 the internal sheath of the penis in the males of many Insects. 

 In the Hymenoptera they are seen as jointed rods, one on 

 either side of the penis. 



The Internal Papillae of the Mesogenital Somite. The existence 

 of two pairs of papillae on the ventral surface of the meso- 

 genital somite in the nymph of the Hymenoptera and Orthop- 

 tera has been sufficiently proved, and Dewitz has shown that 

 the internal papillae are developed from the same source as the 

 external ; but some doubt exists as to the fate of this second 

 pair of papillae. 



Dewitz [375] states that in Locusta they subsequently unite 

 with each other and with the external papillae to form the 

 upper valves of the ovipositor ; and in Apis mellifica he says 

 they form together the large dorsal sheath of the sting, whilst 

 the lateral papillae become its well-known lateral sheaths. He 

 regards the two anterior pairs of papillae as the darts of the 

 sting. It does not appear, however, that Dewitz has actually 

 traced the changes of these papillae, and he has apparently 

 arrived at these conclusions on theoretical grounds only. 



The Ovipositor of Sirex gigas. There cannot be the slightest 

 doubt that the sting in the aculeate Hymenoptera and the 

 ovipositor of Sirex and other boring Hymenoptera are identical 

 structures. In Sirex the dorsal sheath and lancets form a hollow 

 ovipositor, through which the eggs are passed, and these 

 structures correspond with the dorsal valve of the ovipositor of 

 Locusta ; if this is the case, they must be developed from the 

 four papillae on the mesogenital somite. The lateral sheaths 

 of the ovipositor are clearly the homologues of the inferior 

 blade of the ovipositor of Locusta; they also articulate 



