Verhoeff, C. Beiträge zur vergleichenden Morphologie des Abdomens der Coccinelliden, etc. (Archiv f. Naturg., lxi, pp. 1–80, 6 figs., 1895.)
Boas, J. E. V. Organe copulateur et accouplement der hanneton. (Oversigt over det K. Danske Vidensk. Selskab Forhand, 1892, Copenhagen, 1893, 1 Pl., pp. 239–261.)
Pérez, J. De l’organe copulateur mâle des Hyménoptères et de sa valeur taxonomique. (Ann. Soc. Ent. France, lxiii, pp. 74–81, Figs., 1894.)
Goddard, Martha Freeman. On the second abdominal segment in a few Libellulidæ. (Proc. Amer. Philos. Soc., xxxv, pp. 205–212, January 11, 1897, 2 Pls.)
Also the writings of Eaton, Emery, Fischer, Forel, Géhin, Godart, Hagen, Joly, Koletani, Loew, Meinert, Mik, Nicolet, Osten Sacken, Pictet, Roussel, Schaeffer (1754), Schaum, Schenk, J. B. Smith, Thompson, Buchanan-White, Brunner von Wattle-Wyll, Weise, Wyenbergh.
The subject of copulation has been treated by Hoffer, Hartig, Schiedeknecht, Verhoeff, etc.
THE ARMATURE OF INSECTS: SETÆ, HAIRS, SCALES, TUBERCLES, ETC.
Fig. 208.—Larva of Dryocampa rubicunda, stage II.—Bridgham del.
The cuticula.—The integument is externally either smooth and shining or variously punctured, granulated, tuberculated, striated, or hairy. In certain orders the skin is clothed with flattened setæ or scales, while many forms, as some caterpillars (Figs. 208, 209), beetles (Fig. 210), etc., are protected by spines, horns, etc., these in adult insects often forming secondary sexual characters, usually being more developed in the males than in the females.