No. I.] CONTRIBUTION TO INSECT EMBRYOLOGY. 125 



Of the few observations which have been made on the 

 development of the genital ducts in insects, Nusbaum's ('84) 

 are the most important. Their agreement with Palmen's 

 anatomical researches on Ephemerids ('84) has been regarded as 

 sufficient warrant of their accuracy. Nusbaum studied the 

 developing ducts in Mallophaga, Pediculidas, Blattida^, and 

 Culicidae and came to the conclusion that the testes and defer- 

 ent ducts in the male and the ovaries and oviducts in the 

 female are mesodermal, while the seminal vesicles, ejaculatory 

 duct and accessory glands in the male, and the uterus, vagina 

 and accessory glands in the female are ectodermal. He 

 therefore draws the line between mesodermal and ectodermal 

 portions at the juncture of the seminal vesicles and deferent 

 ducts in the male and at the juncture of the oviducts and 

 uterus in the female. This is at variance with my results, 

 since I have found that the seminal vesicles and uterus are 

 mesodermal. These structures are described by Nusbaum as 

 if he had traced their derivation from the ectoderm step by 

 step. Yet he seems not to have studied embryos but only 

 larvae, and it is during embryonic life that the uterus and 

 seminal vesicles are formed. ^ Furthermore his investigations 

 were carried on without the aid of sections. The differentia- 

 tion of the uterus and seminal vesicles from the ectoderm is 

 far from satisfactorily shown in his figures. I cannot therefore 

 regard Nusbaum's work as contributing any evidence in favor 

 of Palmen's view. Palmen concluded from a careful study of 

 the Ephemeridae that the genital ducts of insects originally 



1 This is Nusbaum's description ('84, p. 40) : " Auf der Bauchseite des vierten, 

 von hinten an, Abdominalsegmentes entstehen zwei paarige Hautepithelverdick- 

 ungei) die sich einander nahern um sich dann zu einem hufeisenformigen unpaaren 

 Korper zu vereinigen. Bevor aber noch die Vereinigung zu Stande kommt, losen 

 sich diese Keime von der Haut ab und verwachsen, wie gesagt, mit den Enden 

 der noch soliden Vasa deferentia. ... In dem vorderen Theile des soliden huf- 

 eisenformigen Keimes entstehen zwei vordere geschlossene Hohlen; der mittlere 

 Theil bleibt noch weiter solid, der hintere verlangert sich in zwei seitliche solide 

 Auswiichse. Die zwei vorderen Hohlen verlangern sich nach vorn und differ- 

 enziren sich in die zwei Vesiculae seminales (innere Schlauche) des definitiven 

 birnformigen Korpers. Mit denselben communiciren die sich aushohlenden Vasa 

 deferentia." An essentially similar description is given by Nusbaum for the 

 female (p. 41). 



