TAXONOMY OF MUSCOIDgAN FLIES — TOWNSEND \J 



selection and the pressure of environment. This may be termed con- 

 vergent evolution. Somewhat similar are cases of parallelism, or 

 recurring types of structure in nowise related to one another, which 

 are to be explained by use and adaptation to external conditions. A 

 thorough study of larval and puparium characters will determine 

 such cases beyond a doubt, but in many instances an intimate knowl- 

 edge of the adults will enable one to separate these forms quite accu- 

 rately. Parallel series in the adult of forms of common origin will 

 usually show their distinctness very readily to the experienced eye 

 without a lens. In this way the writer has often made a preliminary 

 arrangement of much material, which subsequent study demon- 

 strated to be correctly separated into distinct forms, many of them 

 so closely resembling each other that they were extremely liable to 

 be confused. A very serviceable guide in distinguishing between 

 forms of common origin is the character and color of the pollen, 

 which is present to a greater or less extent in all the forms. This, 

 strange to say, is extremely constant throughout series of individ- 

 uals of the same form and the same sex. In those forms which pos- 

 sess golden pollen on the head, the male as a rule has the golden 

 shade more pronounced and extensive than the female. The color 

 of the pollen of thorax, and especially that of abdomen, is very con- 

 stant in both sexes. A slight difference in the shade of color of the 

 abdominal pollen, such as that between a silvery cinereous and an 

 ashy cinereous, will frequently serve to correctly separate closely 

 related but distinct forms which might otherwise be confused. It is 

 almost needless to say that reference is here made only to fresh and 

 well-preserved specimens. Greased specimens must be restored be- 

 fore attempting to place them. 



Illustrative of convergent evolution and parallelism, in which adults 

 of tw r o or more forms closelv resemble each other through causes other 



imitated, often has no relation to color, and may even be a miniature or other 

 representation and not the original at all. "Pattern," on the contrary, means 

 the original, to be imitated as to form, size, and color, strictly speaking, and 

 is the term used in mechanics in the exact sense of our concept. 



By using these terms — counterfeit and pattern — we can adhere strictly to the 

 significance of our diction. We would thus speak of an edible counterfeit 

 (species) of an inedible pattern (species), which latter has been unconsciously 

 and involuntarily adopted by the former as a subject for imitation, impelled 

 thereto by certain accruing advantages. Both words express the sense exactly, 

 and both can be used without change as either nouns or adjectives. Deriva- 

 tively, instead of the objectionable term "mimicry," we have the very sugges- 

 tive and thoroughly appropriate name counterfeitism to apply to a subject of 

 rapidly growing importance. It would seem that neither priority nor usage 

 have any claim to consideration in a case of this kind. 



