94 PARTIAL OIUSMOLOGY. 



section 19, for almost all the differences of form there named are to 

 be found in elytra. The same applies to the differences of margin, 

 but with greater limitation. 



Their clothing, also, is so variously different, that scarcely any 

 description of it is found upon the insect body, which does not also 

 occur upon the elytra ; we, therefore, here again refer to the General 

 Orismology. 



The hemelytra, or half corneous wing-cases of the Hemiptera 

 heteroptera, have most qualities in common with the entirely horny 

 elytra. In the majority we can distinguish four divisions separated 

 by furrows, the first three of which are horny, but the fourth forms 

 the membranous portion. The first, the NAIL, ( Clavus, PI. XV. f. ] . ), 

 is a longitudinal almost parallelly sided piece, situated at the interior 

 margin, contiguous to the scutellum, and, in repose, partially passing its 

 sharp edge beneath it ; close to this, upon the exterior, lies the HEM- 

 ELYTRUM (PL XV. f. 1, 6), which is the largest of all the divisions, 

 and forms a triangular horny piece, which enters the mesothorax with 

 its anterior acute angle. The APPENDIX (PI. XV. f. 1. c), which is 

 frequently wanting, follows the HEMELYTRUM; it is likewise a trian- 

 gular, but much smaller, and often right angular horny plate, the 

 right angle of which is contiguous to the exterior margin of the hem- 

 elytra, so that the hypothenuse is turned towards the inner margin. The 

 fourth and last division is attached to this, and which is called the 

 MEMBRANE (membrana, PI. XV. f. 1. d), from its membranous quality. 

 It is generally of a rhomboidal form, with obtuse angles, or it is ovate, 

 but more rarely forming a somewhat reversed half moon. It likewise 

 consists, like all wings and wing-cases, of a superior and inferior layer, 

 between which horny ribs pass, and distend it. 



The pergamentaceous cases, called TEGMINA, differ from the true 

 elytra, by being less firm in their substance, and from the true wings, by 

 their greater strength. They are situated at the same place with the 

 elytra and hemelytra, and they approach nearer to the latter in their 

 structure, but most closely to the true membranous wing. For, 

 although in the hemelytra the ribs and veins are more apparent, yet 

 in the tegmina they are so clearly developed, that they are no longer 

 subject to doubt. Lower, in the anatomy, we shall find that the elytra 

 also possess such veins, but which, from the thickness of their substance, 

 do not become prominent. 



In form, the tegmina are subject to greater differences than the 



