PAIRED SEXUAL OUTLETS 493 



insects behind the 8th, except in the Stylopidae (Strepsiptera), in 

 which they open much in front. 



Figure 464 graphically shows their relation. In the Odonata (F) 

 the chitinous lining or integumental invagination extends inwards 

 where the two oviducts begin, in the Coleoptera (E) the vagina, 

 bursa copulatrix, and receptaculum seminis being lined by a thick 

 chitinous layer. While in Perla the two seminal ducts pass directly 

 into the copulatory organ, in the Coleoptera they open into the 

 unpaired ductus ejaculatorius at a distance from the copulatory 

 organ. 



The morphological results obtained by Palmen, and for the 

 Lepidoptera by Jackson, were apparently confirmed from an em- 

 bryological point of view by Nusbaum, from observations on the 

 development of the sexual passages in two genera of Pediculidse, 

 and are as follows : 



1. The prevalent impression that the larval ducts unite with each other and 

 give origin to the whole system of sexual ducts is incorrect ; they form only 

 the vasa deferentia or the oviducts. 



2. All other parts of the efferent apparatus (uterus, vagina, receptaculum 

 seminis, ductus ejaculatorius, penis, and appended glands) develop from the 

 hypodermis. 



3. The connective tissue and the musculature of the efferent apparatus are 

 derived from mesoblast cells present in the body-cavity. 



4. The efferent ducts originate as paired rudiments. All unpaired (azygos) 

 parts (uterus, penis, receptaculum seminis, unpaired glands, etc.) are at first 

 paired. The unpaired efferent apparatus of insects must therefore be regarded 

 as morphologically a secondary and more complicated form. 1 



5. The male and female efferent ducts are strictly homologous. 



6. The cavities of the oviducts, uterus, vagina in the female, of the vasa 

 deferentia, appended organs, and ductus ejaculatorius of the male arise inde- 

 pendently, and come into connection secondarily. 



The presence of two genital openings, viz. a bursa copulatrix or copulatory 

 pouch, and of the primitive oviducal orifice behind the 9th segment, is peculiar 

 to Lepidoptera, and the inquiry naturally arises whether they represent the 

 outlets of two pairs of segmental organs. The question has been fully set at 

 rest, however, by Jackson, who shows that the copulatory pouch is a secondary 

 invagination of the ectoderm, being derived from the hypodermis, while the 

 second aperture is a special adaptation. It is, however, the partial homologue 

 of the vaginal orifice in other orders of insects. It opens behind the sternite of 

 the 8th abdominal segment, the typical position of the vaginal aperture as 

 shown by Lacaze-Duthiers. The lateral position of the bursa and its separation 



1 Nusbaum's view has been questioned by Heymons, who, from his studies on the 

 embryology of the cockroach (Periplaneta and Phyllodromia) , Forficula, and Gryl- 

 lus, concludes that the ectodermal ends of the sexual outlets owe their origin to an 

 unpaired median hypodermal invagination, and that it is quite doubtful whether the 

 ectodermal portions of the sexual passages of insects were ever paired (p. 104). On 

 the other hand he appears, even throwing out the case of Ephemera, to have over- 

 looked Nassonow's discovery of paired outlets in the young of Lepisma. 



