NO. 14 INSECT ABDOMEN SNODGRASS 85 



fully everted " penis " in this case includes the endophallus, the 

 ectophallus, the phallocrypt, and probably also the shallow genital 

 chamber. 



In the families Nemouridae and Capniidae there appears to be no 

 evidence that the functional intromittent organ is an everted structure. 

 The median exit duct is in some cases short and in others long, and, 

 in species studied, it terminates in an ectophallus, which, however, 

 may be very small. The terminal exit duct of Nemaura vallicularia, 

 as shown by Wu (1923), is a long median tube extending forward 

 almost to the base of the abdomen (fig. 28 H, Dct) ; it is enclosed in 

 a thick sheath of strong muscular fibers, and ends in a short, taper- 

 ing sclerotic penis. Opening into the anterior end of this tube, how- 

 ever, is a much slenderer median duct {dct) that receives the two 

 vasa deferentia, as in Acroveiiria (J, Dej). We might suspect, there- 

 fore, that the large duct of Nemoura is a noneversible endophallus, 

 and that the slender duct is the true ductus ejaculatorius. The internal 

 genital structures of Protoncwoura praecox, as described by Mertens 

 (1923), are the same as those of Nemoura vallicularia except that 

 here the vasa deferentia discharge directly into the large median tube, 

 which latter Mertens says has extraordinarily strong muscular walls 

 and evidently serves to expel the spermatic fluid. A similar, strongly 

 muscular exit passage is present in Taeniopteryx nmura and opens 

 through a wide, bluntly conical ectophallus. The latter is protracted 

 in one specimen observed, but there is no accompanying' eversion of 

 the duct. Wu (1923) describes the development of the exit duct in 

 Nemoura from an invagination of the body wall between the ninth 

 and tenth abdominal sterna, beginning with the ninth instar and 

 increasing in length during subsequent instars. In the earlier stages 

 the vasa deferentia open directly into the median tube, which thus 

 appears in its inception to be the ductus ejaculatorius. A " diphallic " 

 condition is said by Crampton (1918) to occur in Nemoura completa, 

 but since the structures designated " penes " are not demonstrated to 

 be such by dissection, we may suspect that they are merely phallic 

 lobes, and that a single genital orifice will be found between them. 



In the genus Leiictra the phallic apparatus is much reduced, and 

 it appears that the intromittent function may be performed by a pair 

 of processes arising from the sternum of the tenth abdominal segment. 

 These structures are described by Klapaiek in L. nigra and cylindrica, 

 and by Mertens in L. prima and hippopiis as a pair of sclerotic 

 processes (Chitingraten, Titillatoren) arising at the sides of the geni- 

 tal orifice, and embraced by two prolongations of the plates of the 

 tenth sternum. Each median process, according to these authors, is 



