Xl] THE REPRODUCTIVE SYSTEM 215 



The whole capsule is slightly sticky, and eminently suited for the 

 difficult operation of the transference of the sperms externally 

 from the ninth to the second segment. 



The wall of the vas deferens is very thick, being formed of high 

 columnar cells with large nuclei, each of which shews numerous 

 chromatin granules and a conspicuous, deeply-staining nucleolus. 



The genital pore opens mid-ventrally on the ninth sternite. 

 It is guarded by two small chitinous flaps, the valvules, homologous 

 with the valves or lateral processes of the ovipositor in the female. 



2. External Organs (fig. 96). 



The copulatory apparatus of the male Dragonfly is one of the 

 most remarkable structures in the Animal Kingdom. The " palpal 

 organ" on the pedipalp of the male Spider, and the hectocotylous 

 arm of the Cephalopod Mollusc, extraordinary as they are, do not 

 defy all explanation, since in each case they are modifications of 

 an appendage already present. But the apparatus of the male 

 Dragonfly is not homologous with any known organ in the Animal 

 Kingdom ; it is not derived from any pre-existing organ ; and 

 its origin, therefore, is as complete a mystery as it well could be. 

 It is useless to talk vaguely, as some observers have done, about 

 relationships with the Progoneate Myriapods, which have the 

 genital opening far forward on the body. The true genital 

 opening of the male Dragonfly remains far back, on the ninth 

 segment. The copulatory apparatus of the second and third 

 segments has nothing to do with that. It is an entirely new and 

 unique development, for the reception of the sperms, and for theii 

 subsequent introduction into the female. All we can say with 

 certainty is, that its formation is correlated with the great length 

 of the abdomen, with the use of the anal appendages as claspers, 

 and with the adoption of the "tandem" position during pairing. 

 Backhoff [4] has shewn that this apparatus develops late in 

 larval life (at the antepenultimate instar) from originally median 

 unpaired hypodermal cell-masses, which later on assume a 

 bilaterally symmetrical form. Thus it has nothing to do with 

 the lost segmental appendages of the abdomen, which disappear 

 in embrvonal life. 



