143 



the single iníerior appendage (appendix dor.salis of Heymons), 

 of the male is applied to the dorsal surface of the female's head. 



Previous to February 1899 (the date of Williamson's 

 A Note on Copulation among Odonata), systematic descriptive 

 writers had called attention to differences in the shape and 

 structure of the prothorax in the female Z^goptera, and referred 

 to them as correlated with diñerences in the form of the male 

 appendages, and Kolbe (1881) in particular had summed up 

 these correlations. The list of such mutual sexual adaptations 

 in this suborder has been increased during our period b\' various 

 writers, while in consequence of X^'illiamson's discover}- similar 

 adaptations or lacerations on the head of Anisopterous females 

 have been demonstrated or rendered probable, as, for example, 

 by Ris (1910), E. M. Walker (1912), and Calvert (1912). 



CopuLATORY Apparatus of the Males. 



A well-known peculiarit}- of the Odonata, and one which 

 distinguishes them from all other animals except the Araneina 

 and the Cephalopod Mollusks, is the wide separation in the male 

 of the orifice of the ejaculatory duct from the penis and its 

 accessory copulatory structures, the orifice h'ing on the ventral 

 surface of the ninth abdominal segment, as in insects general!}-, 

 the penis, etc., on the ventral surface of the second and third 

 abdominal segments. Before copulation can occur, therefore, 

 the sac, or vesicle, of the penis must be charged with sperm by 

 such a bending of the male's abdomen that the ventral surfaces 

 of its second and ninth segments may be brought in contact. 



The penis and its adjacent accessor}- copulatory structures 

 (described under such names as anterior lamina, vesicle of the 

 penis, genital lobes, etc.) have been utilised for taxonomic pur- 

 poses by many writers, but the investigation of the morpholog}- 

 of these parts lies whoily within the time under our considera- 

 tion. On purely anatomical grounds Miss Goddard (1896) 

 suggested that hamules and penis in certain Libelluline genera 

 are modified abdominal a])pendages of the second and third 

 segments. Thompson, in an almost purely comparative 

 anatomical paper (1908), did not touch on this deeper question, 

 but sought to establish the homologies of the parts found in 



