No. 6J:] DIPTERA OF CONNECTICUT: MORPHOLOGY 95 



as certain Bombyliidae, Cj^rtidae, etc., exhibit a similar modificational 

 tendency, as is also the case with the Phoridae and Lonchopteridae, 

 which occup}^ a '"border-line" position between the orthorrhaphons 

 Brachycera and the Cyclorrhapha, being grouped with the orthor- 

 rhaphons Brachycera by some dipterists, while they are grouped with 

 the Cyclorrhapha by others. We thus hav^e clear-cut evidence of a 

 tendency to develop the "torsional" modifications characteristic of the 

 Cyclorrhapha occurring in their brachyceran precursors (especially 

 in the Dolichopodidae), and a study of these forms readily reveals 

 ho^\- these modifications of the parts in male Cyclorrhapha may 

 have arisen. 



The designation "torsion", as used above, is restricted to the dis- 

 tortion and displacement of the segments instituted by the winding 

 movement or "strophe" of the ninth segment (with the proctiger) 

 which takes place along the sagittal plane of the insect's body, as in 

 the dolichopodid shown in Fig. 12, B, and in certain Cyclorrhapha, 

 etc. A "torsion" thus differs from a "rotation", since the latter term 

 is restricted to a rotation around the long axis of the insect's body, 

 and may involve only the ninth segment, with the proctiger, although 

 the eighth segment may also be involved, as is the case in certain 

 asilids, etc., but in such instances the eighth segment rotates with the 

 ninth (and proctiger) as a unit, and does not lag behind the ninth 

 segment as it does in the torsion movements. 



The torsion inversion of the ninth segment and proctiger of the 

 insects shown in Fig. 12, E and I, (which differs from the rotation 

 inversion occurrinig in male mosquitoes, etc.) apparently represents 

 an arrested stage in the so-called circum version movements of the 

 ninth segment, characteristic of the males of the higher Cyclorrhapha ; 

 and the ninth segment tends to become rigid in the inverted stage in 

 the insects shown in Fig. 12, E and I. In the male syrphids shown in 

 Fig. 12, D and F. Fig. 13, A, etc., the circumversion tendency is con- 

 tinued until the ninth segment hangs down loosely and projects later- 

 ally or three quarters backward, but the ninth segment does not com- 

 plete the circumversion as it tends to do in the higher Cyclorrhapha, 

 so that we may speak of its twisting as a "strophe" (from the Greek 

 word meaning a twisting) rather than a circumversion. In the 

 higher Cyclorrhapha shown in Fig. 13, B^DjF, etc., the ninth seg- 

 ment becomes more rigid as it tends to complete its circumversion. 



The Tenninalia of Male Cyclorrhapha. The following tenden- 

 cies exhibited by the terminal abdominal structures of mnle Cyclor- 

 rhapha are rather characteristic of the group, although they do not 

 necessarily occur in all of the members of the group. These are as 

 follows: (1) The aedeagus extends forward (or downward) in re- 

 pose. (2) The ninth segment, together with the proctiger, (i. e., the 

 composite "gonoproct") undergoes a permanent "circumversion" at 

 the time of pupation (?), and the ejaculatory duct becomes looped 

 up from left to right over the top of the hindgut in all male Cyclor- 

 rhapha thus far observed. (3) The large sternite of the eighth seg- 

 ment tends to become inverted, and its tergite becomes atrophied. 



