INSECT VARIETY. 103 



beetles, butterflies, and moths, as in a grasshopper genus, assume 

 generally masculine differentiation in Orthoptera, indicating 

 dermal alteration and induration ; they are either duplicate, 

 paired, and similarly situate as regards the bodies^ median line, 

 or their development is single, as the alar organ of Leaf-crickets, 

 or quasi unique, as in a family of bugs, and the longicorn 

 beetles, lieciprocating stimulatory friction of articulate parts to 

 express emotion j^ostulates adaptive acquisition," consequent on 

 assumed integumental tendency under attrition to determine 

 a smooth uudulatory surface, and propagation by hereditary 

 transmission, supposing the theory applicable ; any way, a 

 rudimentary structure of this description exists in the Stag 

 Beetle at the inferior and posterior extremity of the head ; 

 and whenever a member or group of insects is capable of 

 music, we may establish a degradation of the organs almost 

 invariably in mute individuals of the opposite sex, or in 

 other members of the genus or family. Practically, the micro- 

 scope establishes the essential constituent, the file or Ihiia, to be 

 a dermal or skin excrescence, with a systematic exaggeration or 

 coalescence of its external callosities, wrinkles, tubercles, or a 

 protrusion of the spiral thread of the wing- veins or other 

 tracheal organ (Plate III., Fig. 7; Plate II., Figs. 4 and 7). 

 Theoretically, this active or passive source of sonorous vibra- 

 t'on is a variously-placed more or less f shaped tumour, 

 provided with denticulations more or less regular, which are 

 vibrated and sounded diagonally over a narrow raised callosity 

 or ridge, on the chitinous integument or modified alar vein. 

 These latter, coustituting the passive or active clasping organ, 

 assume the function of a violin bow or plectrum. 



The musical organ^'s existence in four orders of Insecta has 

 been ascertained, and it attains a maximum, with structural and 

 functional perfection, in the mandibulate tribes. Thus while the 

 musical instruments emit but faint sounds, or monotonous creaking 

 indicative of fear, or at most of anger, in genei'aof beetles, butter- 

 flies and moths, bugs and bees, in some Lepidoptera and 

 beetles, and in most Orthoptera where they are accompanied 

 with membranous adjuncts and generally differentiated to the 

 males, they become capable of mutually intelligible modulation 

 by variation in the direction, force, or length of their stroke, so 



