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 Papille of the Mesogenital Somite.-—The existence 
of two pairs of papille 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 papille. 
Dewitz [875] states that in Locusta they subsequently unite 
with each other and with the external papillz 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 papilla 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 
