178 I June, 



all I shall wish to imply, wheu speaking later on o£ the suppression 

 of a plate, will be that the usual deposit has not taken place, and not 

 that the membrane itself is absent. In a few insects, like Elachista 

 cygnipennella (see figure post.), the plates are broad, substantial pieces, 

 not so very unlike the plates of an abdominal segment, with which 

 they are morphologically identical. In others, again, as Coleophora 

 ccBspititiella (see figure post.), they are long and narrow ; whilst in 

 one or two others of this genus, of which I have preparations before 

 me, the plates are so narrow that they are barely as wide as their rods, 

 and cannot well be distinguished from them. But in the great mass 

 of insects these chitinous pieces are plates only in name, for they are 

 broken up into fine lines or threads, which in some instances are 

 armed with numerous cross spiculse, and form very beautiful objects 

 under the microscope. 



Although the plates are, as I have said, identical with those of an 

 ordinary segment, ihey are differently put together in the two cases. 

 Taking an ideal segment to consist of four pieces, we find that in an 

 ordinary segment the two upper pieces are united to forui the dorsal 

 plate, and the two lower the ventral plate ; whereas, in the ovipositor 

 an upper is united with a lower piece to form a lateral plate, the result 

 of the combination being that the orifice of the ovipositor lies in a 

 vertical plane, and not in a horizontal one as we should have expected 

 from the general structure. But before dismissing jhis part of the 

 subject, we must glance for a moment at the very exceptional state of 

 things in the plant-cutters. We have just seen how attenuated the 

 skeletal portion of the ovipositor becomes in very many insects, but 

 in these others it undergoes quite an opposite change, and is developed 

 into a single, but very large and powerful plate, fitted for cutting or 

 piercing the tissues of plants. Its position is 1 orizontal, with the 

 visceral tube suspended from the under-side ; ani from this relation 

 of the parts we must conclude that it represents the dorsal plate of 

 an ordinary segment, the ventral plate having tp all appearance been 

 suppressed, or being represented in a few of them, as for example in 

 Micropteryx by a pair of isolated pieces of chitine lying in the lower 

 side of the wall of the visceral tube. 



In the previous communication [ spoke or the rods as dorsal and 

 ventral. This is misleading, for their true relationship is with the 

 segment as a whole, and not with a part of it. The one pair, which 

 we will now call the outer pair, work the Stl; segment or its equivalent, 

 the sheath ; and the other, or inner pair, work the ovipositor or 9th 

 segment. The rods are to aJl intents and purposes prolongations of 



