142 Mr. A. B. Eaton on 



cus. In Baetis,% Burm.^ and in Baetis, Leach, the egg- 

 valve takes the foi'm of an entire membrane^ and arises 

 from an extensive transverse base ; the same organ is 

 bifid in the subgenus Gloiion of the genus Ba'et'ts, Leach. 

 Its serial homologue is the "last ventral plate ^' of 

 Baetis,X Burm., and the so-called '^ egg- valve" oi Bota- 

 manthus [Le-ptophlehia) of Dr. Hagen's Synopsis of the 

 British Bphemeridoe. 



Of the Ortlioptera possessing the ovipositor Bcticus 

 verrucivorus, Lin., may be taken as an example. In this 

 insect the instrument in question seems at first sight to 

 be simply bivalvular ; but upon a close inspection each 

 valve is found to be made up of three elements inti- 

 mately adhering to one another. On dividing the 

 lamina subgenitalis longitudinally it will be seen that 

 the first pair of elements proceeds from the middle of 

 the apex of the eighth ventral arcus ; this pair (cnnato- 

 tergo-rhabd'ites, Lac.-Duth.) , is therefore specially homo- 

 logous with the terebra. The remaining pairs, the val- 

 vulse vaginales externge {ennato-episternites and ennato- 

 sterno-rhahdites anchylosed, Lac.-Duth.), and valvulas in- 

 ternee [ennato-sternites or gorgerets, Lac.-Duth.), maintain 

 positions with respect to the first pair and to each other 

 corresponding with those occupied by their special ho- 

 mologues in Agrion. Being more intimately adherent to 

 the outer valvule than the terebral elements, and being 

 moreover covered by them, the inner valvulee are demon- 

 strated with greater difiiculty than the other pairs of 

 elements. Their limits are however indicated by a 

 shallow groove which runs almost to the acute apex of 

 each outer valvula on the inner side ; and on cutting 

 across the valves each element seems to be provided 

 with a special ti-acheal tube. As Fischer (Orthop.Eurbp. 

 p. 21) ascribes a simple bivalvular ovipositor to BJiaphi- 

 dophora cavicola, KoL, it may be surmised that a more 

 complete union obtains between its components, than is 

 arrived at in Beticus. 



It is not possible at present to determine exactly the 

 homologies of the ovipositor of Hyincuopfera in every 

 family, because the mode of its development has not yet 

 been observed with sufficient care (so far as I am aware) 

 in any group other than the Acideata. In describing 

 the sting I shall employ the terms used to denote the 



X This symbol distingiiisbes a misaiDplied name. I propose to call this 

 geuus Ecdyonuriis. Type, E. venosus, Fabricius. 



