NO. 8 INSECT ABDOMEN SNODGRASS I9 



chamber, finally, may take the form of an elongate sac or a slender 

 tube continuous with the oviduct (D). In such cases the median 

 egg passage consists of an anterior part (Ode), which is the true 

 oviduct (Eiergang), since it serves only for the conveyance of the 

 eggs, and of a posterior section appropriately distinguished as the 

 vagina {Vag). The two parts are separated approximately by the 

 opening of the spermatheca into the anterior end of the vaginal 

 region of the tube. 



On the venter of the ninth abdominal segment there is commonly 

 formed a third median invagination, which gives rise to the accessory 

 glands (fig. 4 B, AcGl). The opening of these glands may be included 

 in the genital chamber by the posterior extension of the eighth sternum, 

 but it always lies between the bases of the ovipositor blades of the 

 ninth segment when an ovipositor is present. 



The observations of Metcalfe (1932a) on the manner by which 

 the median oviduct becomes extended from the seventh to the eighth 

 segment in Philacnus are somewhat different from those of George 

 (1929) on the same insect and of Nel ( 1930) in Acrididae. According 

 to Metcalfe there is formed primarily in Philacnus spunmrius an 

 oviducal invagination behind the seventh sternum, and a " uterine " 

 invagination behind the eighth sternum. The second extends forward 

 and overlies the first. Then the anterior opening becomes closed, and 

 the "opposing walls of the two invaginations come into contact, unite, 

 and eventually break down, thus establishing a continuous median 

 passage opening posteriorly through the primary " uterine " aperture 

 behind the eighth sternum. The anterior end of the " uterine " in- 

 vagination, which does not unite with the oviduct, becomes the func- 

 tional sperm receptacle of the adult. It seems probable that the " uter- 

 ine " invagination observed by Metcalfe represents both the true 

 spermathecal rudiment and the genital chamber invagination of orthop- 

 teroid insects, which latter may become a vaginal section of the 

 definitive egg passage. 



In all Orthoptera and Hymenoptera and probably in most Hemip- 

 tera and Diptera, the egg exit is the secondary opening of the median 

 oviduct established on the eighth segment, or in the intersegmental 

 membrane behind the eighth sternum. This opening, the true gono- 

 pore, however, is usually concealed by an extension of the eighth 

 sternum, or of the seventh sternum ; and it niay be carried inward 

 within a copulatory invagination having the form of an open genital 

 chamber, or of a tubular vagina, in which case the functional genital 

 aperture is the vulva, that is, the external opening of the genital cham- 

 ber or vagina. 



