iS'Jl.J 



213 



:xsh^ 



07 pi 



Fig. 6. 



case, clue to the size and ihickiiess of the 

 plates in all tlie segments, exce))t the first, 

 which, on the contrary, is weak and almost 

 entirely membranous, in order to enable 

 the insect more readily to curve her body 

 round into the position assumed in laying. 

 The 7th segment (see Fig. 5) is remarkable 

 in several ways. In the first place its 

 lower plate projects considerably beyond 

 the upper, forming by itself the tip of the 

 abdomen — a most unusual feature, and 

 only to be found in these insects. It is also 

 of great size, the dorsal plate equalling in 

 length the 6th and 5th segments together, and the ventral almost the 6th, 5th, and 4th; 

 the latter is besides very deep and capacious, and turns up behind in a rather sharp 

 curve, which ends in an overhanging lip. A fringe of very long tactile hairs comes 

 from under the lip, and others are scattered over the tip of the dorsal plate, none 

 being found in either of the usual situations — the sheath and the ovipositor. 



The egg-laying organs are of surprising size, and the rods reach, when retracted, 

 to the junction of the 3rd and 4th segments. On removing the external case, the 

 object that appears most conspicuously is a large chitinous 

 plate that was lying close under the upper wall of the 

 abdomen. This is the sheath — an imperfect structure in 

 one sense, as it consists only of the dorsal plate, the ventral 

 being obsolete. It is of great length, being only one-third 

 less than its rods ; and may, for convenience of description, 

 as well as to mark a distinct difference, be divided into two 

 unequal parts, of which the inner is about twice as long as 

 the outer. The inner portion (8 (sh.l) ) is merely a slightly 

 arched plate, having the outer rods inserted into its corners. 

 Its chief function seems to be to support the inner I'ods, or 

 rather the plates into which ihey expand, and prevent their 

 bowing out under the great muscular strain to which they 

 are exposed ; whilst a more subsidiary use may be to 

 strengthen, when the instrument is protruded, the weak 

 spot in the outer wall occasioned by the shortness of the 7th 

 dorsal plate. In the case of the outer and shorter portion 

 (8 (sh. 2 ) ) it is to be noticed that it is compressed laterally, 

 or pinched in, as it were, so that, whilst it becomes much 

 narrower across the back, it is correspondingly deepened at the sides, the cross 



pli.m- 



Fio. 5. —The end of' the abdomen in A. viridella. 



Fig. 6. — Side view of the point of the ovipositor, and of the outer portion of the sheath, 

 ov. pi., Trowel-shaped terniinati(ju of ovipositor, v. t.. Flaps of the visceral tube, 

 sh. pi., Plate portion of the sheath, sh. m., Membranous portion of sheath. 



Fig. 7. — Dorsal view of the sheath «nd point of the ovipositor; the four rods broken off .short. 

 8 (sh. 1), Inner portion of sheath, a (sh. 2), Outer portion of sheath. Other letters as 

 in Pig. 6. 



