52 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 94 



virtually a part of the definitive first valvifer, by which the latter 

 articulates w^ith the ninth tergum ; but the sclerite acquires also a 

 flexible union with the second valvifer {2Vlf), which gives the two 

 valvifers on the same side a point of motion on each other. This 

 same structure and mechanism occurs in other members of the same 

 family (I, J, K). In the Gryllidae, therefore, the definitive first valvi- 

 fer is a composite plate formed of the true first valvifer and of a small 

 dorsal sclerite derived from the coxopodite region of the ninth seg- 

 ment, and thus acquires its secondary articulations with the ninth 

 tergum and with the second valvifer. In the Tettigoniidae the valvifers 

 have a simpler structure, and in the nymph (fig. 21 D) each is a small 

 plate {iVlf, 2Vlf) in its respective segment; those of the first pair 

 are entirely separated from the small eighth sternum (VlllStn). 



It will now be of interest to study the development of the ovipositor 

 in a member of the x\crididae in order to discover if possible the nature 

 of the disparity, so evident in the adult structure, between the acridid 

 type of ovipositor and that characteristic of other insects. In a very 

 young nymph of Melanoplus (fig. 22 A) the ventral plates of both 

 genital segments are well developed and of approximately equal size. 

 Rudiments of the first valvulae are evident as a pair of flattened lobes 

 {iVl) slightly protruding from behind the sternum of the eighth 

 segment ; but the third valvulae {3VI) already have the form of small 

 conical processes arising from the posterior part of the ninth sternum. 

 Here, then, we encounter again the same differences in the relations 

 of the valvulae to the sternal plates as w^as observed in Gryllidae and 

 Tettigoniidae, namely, the origin of the first valvulae behind the 

 sternum of their segment, and that of the third valvulae directly from 

 the sternal plate. At a later stage in the growth of Melanoplus (B, C) 

 the first valvulae have become conical processes, and the small second 

 valvulae (C, 2VI) have appeared between the bases of the third val- 

 vulae. From this stage to that of the adult but few external changes 

 take place in the ovipositor. The intervalvular sclerites are developed 

 medially before and behind the bases of the valvulae of the ninth 

 segment, the ninth sternal region becomes otherwise reduced, while 

 the eighth sternum increases its length and acquires a small median 

 process on its posterior border, which is to be the egg guide. The 

 valvulae take on the form characteristic of the adult, and those of 

 the first and third pairs become densely sclerotic in the mature insect. 

 The acridid ovipositor is thus seen to be an organ formed entirely 

 of the valvulae, there being no dififerentiation of valvifers in the cox- 

 opodite areas of either genital segment. In the eighth segment the 

 coxopodite areas must lie in the membrane behind the eighth sternum 



