ENEMIES OF APHIDES. 41 



tion of the upper, or inner, surface seems to show that the mem- 

 brane is not divided. But on examination by transmitted light, 

 and particularly in a transparent medium, such as Canada balsam, 

 and after treatment by potash, a chitinous division is very appa- 

 rent, and it becomes clear that we have to do with an organ which, 

 although perhaps not actually bilobular, approaches so nearly to it 

 as to have caused observers (viewing it in a transparent condition) 

 to conclude at once that it presented a definite Orthopterous 

 character of genuine significance. The chitinous rigidity, how- 

 ever, is very different to the fleshy organ of the cricket (PI. T., 

 Fig. 6) and similar Orthoptera, while the structural arrangement 

 of the parts presents no analogy, and although an approach to the 

 orthopterous central division must be admitted, it is by no means 

 clear that the structure of the labium as a whole is such as to 

 support any ordinal transference of the genus. 



For better comparison of these organs with those of the Orthop- 

 tera, I have figured upon PI. I., at Fig. 6, the labium of the 

 House Cricket, which, it will be observed, is a thick fleshy organ, 

 supported on a muscular and flexible column, and provided with 

 muscles beneath the frontal lobes, by which they are controlled. 

 And on PI. II., at Fig. 5, may be seen the drawing of the 

 labium of the Common Earwig, in which the organ is so com- 

 pletely divided and altered in character, that it assumes the form 

 of two thickened single-jointed palpi. The fleshy lobes of the 

 Cricket present some slight resemblance in shape to the same 

 organ in certain of the Diptera, although, of course, without the 

 trachea-like tubes so characteristic of the latter, and neither they 

 nor the isolated palpus-like labium of the Earwig present any 

 resemblance to the mouth-organs of either section of the Neu- 

 roptera. 



The characters afforded by the wing venation, which were the 

 basis of the original Linngean classification, appear to me to indi- 

 cate very forcibly the unity of the order. On PL I., at Figs. 

 3 and 4, I have figured the wings of Calepteryx and of Stalls, the 

 whole of the inner or secondary nervures being omitted, in order 

 to show the similarity of the principal nervures in these, the most 

 diverse genera of the two sub-orders. The same main nervures 

 may be traced without difficulty in Libellula and in Chrysopa, and 



