DEVELOPMENT OF THE MALE GLANDS 579 



the mesodermal rudiments, while the other parts of the sexual 

 efferent apparatus (uterus, vagina, receptaculum seminis, ejacula- 

 tory duct, penis, and all the accessory glands) develop from the 

 integumental epithelium and are of ectodermal origin. In fact, 

 the unpaired parts (uterus, penis, receptaculum seminis, unpaired 

 glands) have developed from paired rudiments, being outgrowths of 

 the hypodermis. The hinder portions of the rudiments of the sexual 

 glands approach these hypodermal growths and fuse with them. 

 Through a median fusion of the paired hypodermal growths arise 

 the germs of the unpaired organs. These observations are in com- 

 plete agreement with the results at which Palmen arrived by 

 anatomical investigation (see p. 492). 



From the agreement of the position of the sexual openings in 

 Phyllodromia with the conditions observed in the Ephemeridee, with 

 which the Perlidae also agree, we conclude that in the entire group 

 of insects an opening between the 7th and 8th abdominal segments 

 is the primitive condition, and that only by a secondary shift- 

 ing has a more posterior position of the opening (in many forms) 

 been brought about. In this category we must certainly include 

 the Thysanura, in which the sexual opening is single and situated 

 between the 8th and 9th abdominal segments. 



Development of the male germinal glands. These rudiments arise 

 in exactly the same manner as those of the female. Sexual differen- 

 tiation takes place in the later embryonic stages. We then notice 

 that in the male four masses of genital cells become surrounded by 

 epithelial cells. These masses, which form the germs of the four 

 testicular follicles of Phyllodromia, stand in intimate union with 

 the rudiment of the vas deferens, and in the later stages move in 

 connection with the latter, away from and behind the original 

 genital rudiment. There remains, then, with the terminal thread- 

 plate a remnant of the genital rudiment, which, according to Hey- 

 mons, forms the female part of the original hermaphroditic genital 

 rudiment, and in special cases may develop even into rudimentary 

 egg-tubes and eggs. The rudimentary organ arising out of this 

 genital rudiment may also be demonstrated in the adult male of 

 Phyllodromia. 



In the female the oviduct arises directly out of the originally 

 established efferent passage. In the male, on the contrary, it is 

 not, along its whole length, transformed into the vas deferens, but 

 its distal terminal portion degenerates and is replaced by a newly 

 formed terminal portion of the vas deferens, which then unites with 

 the ectodermal ductus ejaculatorius. (Korschelt and Heider.) 



