84 Rev. F. D. Morice 07i male terminal segments and 



fashion (especially towards its base), and much move 

 thorougldy chitinized in certain places (especially aloncf 

 its inner margin and all over its basal part) than elsewhere. 

 All the appearances in it of tooth-like processes, etc., are 

 really produced hy foldings of the substance, foreshortened 

 in various ways according to the point of view. In fact 

 the whole apparent structure of the object as viewed in 

 the flat field of a microscope is simply a mass of optical 

 illusions. Still the phenomena themselves, however de- 

 ceptive, are constant in each species, and can therefore be 

 used to furnish us with specific characters, if we have 

 sufficient familiarity with microscopic work not to be 

 misled by the etSwAa of the " optic glass." 



When the armature is viewed from behind, a curious 

 object with a bifid or bilobed apex appears to protrude 

 from the inner side of eacli stipes, close to and partly 

 covering the bases of the saoittse. This is called the 

 volsella. It has in some points of view the appearance of 

 a distinct organ, j^artly imbedded in the stipes, but I think 

 it is really only a peculiarly folded portion of the stipes 

 itself — at any rate I have never succeeded in removing it 

 without bringing away part of the stipes with it. The lobes 

 at its apex differ in shape and size a good deal in different 

 species (PI. IX, 41, 42, 43), and might give good 

 characters if they Avere more conveniently placed for 

 examination. Sometimes they are pretty conspicuous 

 even in the dorsal view of the armature, but more usually 

 they are hidden by the dilatations of the sagittal. The 

 opposing faces of the lobes seem to be covered with rasj^- 

 like denticulations or tubercles, and I think they must 

 have some prehensile function, but they do not seem to 

 have any power of movement apart from that of the stipes 

 as a whole. 



The armatures which I have figured are rendered semi- 

 transparent by immersion in Canada balsam. This causes 

 a pair of divergent rod-like, perhaps tubular, objects to be 

 seen indistinctly through the surface of the stipites, which 

 on dissection are found to proceed from the bases of the 

 sagittae, and are part — I suppose — of the apparatus by 

 which the latter are moved. (I have not attempted to 

 take characters from them, as they cannot be seen without 

 special preparation of the armature.) 



Such of my figures as represent neither armatures 

 nor seventh ventral plates arc intended to render more 



