222 Journal New York Entomological Society. f^'°'- -"^^J- 



now m such a state of fusion that their discernment is rendered a 

 matter of some difficuUy, requiring the use of a compound microscope. 



For many years the Acalyptrate Muscidse have been Hned up in 

 two groups according to the course of the auxiHary vein. The dis- 

 tinctness with which this vein is separated from the first longitudinal 

 is at most a matter of relativity, but since the auxiHary vein is an 

 ancestral relict in a modern group of insects, its course does serve 

 to interpret phylogeny. Heretofore the auxiliary vein has been cur- 

 sorily looked at and has been accounted absent when there is no dis- 

 tinct chitinization. A close examination, both by transmitted and by 

 reflected light, reveals a fold in the wing membrane even where the 

 vein is lacking, and thus the former course of the vein can be deter- 

 mined. For exactness this part of the wing must lie flat in the field 

 of vision. Moreover, the costa is frequently broken at the end of the 

 auxiliary vein, whether the vein itself is present or not, and, therefore, 

 the exact position of the costal break affords a valuable clue to the 

 ancestral history of these flies. Just beyond the humeral crossvein 

 the costa may be again broken, clearly discernible by transmitted light, 

 the break occurring where some of these flies, such as Stcgana and 

 Drosophila, still fold down their wing. A distinct break at this place 

 is characteristic of the Milichiince, Drosophilinse and Ephydrinae, but 

 does not occur in any of the Agromyzinae, Ochthiphilinse, Geomyzinse, 

 and several of the other groups. As a single character this costal 

 fracturing is probably as weighty as any. 



The lengths of the crossveins as compared with the segments of 

 the longitudinal veins, the proportions of the sections of the costa, and 

 the course and termination of the longitudinal veins are all variable 

 within certain limits, but are useful characters for less than generic 

 determination. The shape of the calypter and the character of its 

 fringe of cilia, the form of the alula and of the anal angle of the wing, 

 the extent of the basal cells and of the anal vein, the position of the 

 crossveins, the origin of the third vein, the strength of the fourth and 

 fifth veins in particular, the hairiness of the basal section of the costa, 

 all offer characters of more than generic value, probably having been 

 under less rigorous selection than structures in the outer part of the 

 wing. 



Naturally, chaetotaxy is important here, as it is in related Muscidae. 

 Not onlv the number of bristles and their exact location but even their 



