210 GENITALIA OF MALE DIPTERA AND MECOPTERA 



secondarily ventral by being twisted around their long axis 

 (they revolve as a whole, not singly). In primitive sawflies the 

 parts remain in their normal position, and thus enable us to 

 determine the original relations of the parts, and to homologize 

 them with other insects. Bearing these facts in mind, I would 

 call attention to the following modifications of the parts in male 

 sawflies, which throw considerable light upon the interpretation 

 of the genital structures of the Diptera and other higher insects. 

 In some sawflies, median portions of the basal segments of 

 the genital styles become detached from their respective segments 

 and approaching one another, unite to form a median interbasal 

 plate (interbasis or connective) or median plate primitively 

 situated above the penis valves (intromittent organs), although 

 in some sawflies, the plate in question appears to be below the 

 penis valves, since a secondary torsion of the parts causes the 

 plate to lie below the penis valves when the genital apparatus 

 turns over (through one hundred and eighty degrees). In the 

 sawfiy shown in figure 3, the connective or interbasal plates, 

 labeled ib, are partially detached from their respective basal 

 segments gs, and tend to unite in the median line of the genitalia 

 — a process which is completed in certain sawflies. In the Dip- 

 teron shown in figure 7, there occurs immediately above the 

 intromittent organ ae, an apron-like plate ih which is connected 

 laterally with the leases of the genital styles gs, and from its 

 position above the intromittent organ and between the bases of 

 the gonostyli it apparently represents the united interbasal 

 plates ib of the sawfiy shown in figure 3 (albeit, in the sawfiy in 

 question, these plates have secondarily come to lie below the 

 intromittent organ, as in the higher sawflies — but not in the 

 lower ones). On the originally ventral (but secondarily dorsal) 

 surface of the genitalia of the sawfiy shown in figure 8, two 

 slender structures labeled vv (which may possibly represent the 

 so-called volsellae of higher Hymenoptera) become detached 

 from the median portions of the basal segments of the genital 

 styles gs. The small genital ossicles labeled s in the sawfiy 

 shown in figure 8 (which may possibly represent the so-called 

 sagittae of higher Hymenoptera) , are also ai)parcntly detached 

 portions of the basal segments of the genital styles gs, which 



