180 THE CANADIAN ENTOMOLOGIST 



sternite of the ninth segment is a structure of considerable interest from the 

 fact that in the higher orders it forms the hypandrium "O""' (Fig. 3) or ventral 

 plate extending below the genital, apparatus of the male insect, and its form 

 and development offer features of some value in classification. 



Behind the ninth sternite, or hypandrium "\f" (Figs. 4 and 5) ot tlu' 

 Ephemerida, there occurs a plate formed by the union of the "coxites" or styligers 

 "a" and "a," which represent the basal segments of the gonopods or styli bear- 

 ing the labels "b" and "c." The plate "a" and "a" of Fig. 4 is usually in- 

 terpreted as the tenth sternite by students of the Ephemerida (Morgan, Eaton, 

 etal.); but Handlirsch, 1913, (Handb. der Entomologic) figures the terminal 

 stru("tures of a male ei)hemi'ri(l Palin^^oiia, in which the styligers ol "coxites" 

 (i.e., tin' jjarts labeled "a" in Fig. 4) are seiiaralc and distinct, and Walker, 

 \^)\\) (1. c.) also points out that these "coxites" or sl\'ligers ma\' unite to form 

 the plate "a" and "a" behind the ninth sternite in the Ephemeridii (iMg. 4). 

 This interpretation is apparenth- the correct one, and has been a(io[)lt-d in the 

 present discussion. 



Between the styli or gonopods labeled "b" and "c" in Figs. 1 and "> ol the 

 Ephemerida, there occurs a pair of penisvalva' "d," through which the ejaculatory 

 ducts open. In some insects, the common opening of the united ducts is located 

 at or near the base of the penis valves. It is quite possible that the penis valves 

 "d" represent the endojKKlites (inner branches) of a pair ol abdominal liml)s 

 whose exopodites (or outer branches) are represented by the st\li or gonopods 

 labeled "b" and "c" in Figs. 2, 3, 4, etc. If this be correct, both the penis 

 valves and the gonopods would have to be regarded as belonging to the same 

 segment (the ninth) since they are parts of a pair ol limbs borne on one seg- 

 ment. This interpretation has a direct bearing on the view that the inner and 

 the dorsal valvulje of the ovipositor of the female also represent the endopodites 

 and exopodites of a pair of abdominal limbs, since it is quite possible that the 

 penis vaKes of the male insect are homologous with the inner valvuke ol the 

 Ovipositor of the female; and the gonopods or styli of the male are homologous 

 with the dorsal valvulie of the ovipositor of the female insect. The penis xaKes 

 of the male and the inner valvulae of the ovipositor of the female would represent 

 endopodites, while the styli (or gonopods) of the male and the dorsal valvuUe 

 of the ovipositor of the female would represent exopodites of a pair of abdominal 

 limbs borne on the ninth segment in both cases, according to this \iew; but 

 Wheeler, 1893, (Jour. Morphol., \'III, p. 1) maintains that the inner \al\uhe 

 of the o\'ipositor, for example, are in realit\' styli orioinally borne on the tenth 

 sternite, and are only secondarily located on the ninth sternite as the result ol 

 their migration to their final position between the dorsal \-alvuhe (of the o\i- 

 positor) which are located on the ninth sternite. If this be correct, the inner 

 valvuhe of the ovipositor (and their supposed homologues, the penis \al\es ot 

 the male) do not originate on the same segment with the dorsal valvuUv ol the 

 ovipositor (or their supposed homologues, the gonopods or styli of the male), 

 and therefore cannot be regarded as the endopodites of a pair of limbs whose 

 exopodites are represented by the dorsal valvuUe (since the two branches of a 

 biramous limb cannot originate on separate segments). 



Wheeler, 1S93, (1. c.) would interpret the three pairs of NaKuhe comjiosing 

 the ovipositor of a female insect, as three pairs of modified styliform appendages 



