GENITAL ORGAN'S. 349 



In later stages the genital rudiment shortens considerably, so that it is then 

 restricted to a smaller number of abdominal segments than at first. The 

 separate ovarian tubes at the same time pass from their original vertical position 

 and become more horizontal. 



The paired insertion of the rudiment of the oviduct into the 

 hypodermis of the intersegmental furrow between the seventh and 

 eighth abdominal segments recalls conditions observed by Palmen in 

 certain Ephemeridae, in which the paired aperture of the genital 

 efferent ducts is retained throughout life. This is the original 

 condition in the Insecta. In the female of Phyllodromia, the un- 

 paired terminal section of the genital passage develops during larval 

 life from an ectodermal invagination, a genital pouch forming in 

 which the egg-cocoon is carried. This genital pouch is formed, as 

 Haase has proved, through the invagination into the interior of the 

 body of the chitinous sternal plates of the eighth and ninth ab- 

 dominal segments. 



"With regard to the development of the efferent genital ducts in 

 the Insecta, we must refer to the results obtained by Xusbau.m 

 (Xo. 61) and Palmen (Xo. 162), which fully agree with those here 

 mentioned as obtained by Heymoks for Phyllodromia. 



Xusbaum studied the development of the efferent ducts in 

 Pediadina and Periplaneta. He found that only the vasa deferentia 

 or the oviduct is derived from the posterior portions of the genital 

 rudiment, i.e., from mesodermal structures, while the rest of the 

 efferent apparatus (uterus, vagina, receptaculum seminis, ductus 

 ejaculatorius, penis, and all the accessory glands) develop from the 

 integumental epithelium, and are therefore of ectodermal origin. 

 The unpaired portions (the uterus, penis, receptaculum seminis, and 

 unpaired glands) develop out of paired hypodermal rudiments. The 

 posterior strands of the genital rudiments become applied to the 

 hypodermal growths just mentioned and fuse with them. A fusion 

 in the middle line of the paired hypodermal growths gives rise to the 

 rudiment of the unpaired organs. These observations agree entirely 

 with the results obtained by Palmen from the standpoint of com- 

 parative anatomy. Palmen found the most primitive type of efferent 

 ducts in Heptagenia (an Ephemerid), an unpaired section being here 

 altogether wanting. The oviducts open separately into the fold 

 between the seventh and eighth abdominal segments, while the vasa 

 deferentia open into a paired penis on the posterior margin of the 

 ninth sternite. An unpaired section may develop from this paired 

 rudiment in individual cases ( $ Forficula, Meinert) through defective 



