128 EMBRYOLOGY OF INSECTS AND MYRIAPODS 



slender tube continuous with the oviduct. On the venter of the ninth 

 segment there is commonly formed a third median invagination, which 

 gives rise to the accessory glands, the openings of which may be included 

 in the copulatory pouch. 



That the embryonic vasa deferentia of the male Orthoptera end pos- 

 teriorly with hollow terminal enlargements, or ampullae, inserted into the 

 appendage rudiments of the tenth abdominal somite has long been known. 

 The cavities are present in the ampullae long before the lumina appear in 

 the other parts of the ducts. The ampullar cavities are ventral remnants 

 of the coelomic sacs of the tenth abdominal somite, and similar though 

 transient ampullae of coelomic origin may occur in the preceding abdomi- 

 nal somites. To the ampullae of the tenth segment of the male, however, 

 are attached the posterior ends of the genital strands that become the 

 vasa deferentia. The ampullae persist first as terminal parts of the 

 lateral ducts but later united as an anterior part of the definitive median 

 ejaculatory duct, the posterior part of this duct, however, being of 

 ectodermal origin. 



According to Wheeler's (1893) account of the development of the 

 genital ducts in Conocephalus, the embryonic female ducts, which likewise 

 terminate with ampullae, end in the appendage rudiments of the seventh 

 abdominal segment, but there is also a pair of ampullae in the tenth-seg- 

 ment appendages, which appear to be homologues of the male ampullae. 

 The account of Heymons (1890, 1895) of the ducts in Dermaptera, 

 Blattidae, and Gryllidae is essentially in agreement with that of Wheeler 

 for Conocephalus in so far as the male ducts are described as terminating in 

 mesodermal ampullae in the tenth segment and the female ducts in 

 ampullae of the seventh segment. According to Heymons, however, 

 there is evidence of a primary branching of the ducts in each sex to both 

 the seventh and the tenth segments. Wheeler, on the other hand, 

 believed that male insects never have ampullae or branches of the genital 

 ducts in the seventh segment. Heymons' illustration of Forficula gives a 

 convincing example of the branching of a genital duct to the two seg- 

 ments, but his identification of the posterior branch as the definitive 

 oviduct is evidently wrong, since the definitive female ducts in Der- 

 maptera open on the seventh segment. 



In the Apterygota the gonads likewise form from the splanchnic meso- 

 derm. The duct from the gonad which passes through the fourth segment 

 is also formed from the splanchnic layer. Since the gonad is ventral in 

 position in Isotoma, differing in this regard from the pterygotes, a terminal 

 filament is lacking. 



A more detailed summary of the development of the reproductive 

 organs, especially with reference to the morphological implications, is 

 given by Snodgrass (1933, 1937). 



