14 ENTOMOLOGICAL NEWS [Jan., '14 



occurrences. Transitional individuals or means of variation 

 occur linking together extremes of variation that seem to have 

 been derived from the same specific stock. The extremes need 

 names if they are abundant enough in individuals to constitute 

 form-occurrences ; so do the means if they are similarly abun- 

 dant and capable of characterization. But isolated transitionals 

 and those of slight differentiation may be recorded by noting 

 their degree of divergence from one or other of the named 

 forms. In this manner exact and concise records are pre- 

 served of each individual form and its variations. Such rec- 

 ords are indispensable in both present and future work. These 

 forms are in many cases potential if not actual species, and all 

 of them need to be recorded now. 



The lumping of recognizable forms under one name is a 

 most serious taxonomic offense, unless in each case the precise 

 limits of divergence from the typical form are shown. An 

 immense number of muscoid names has been thrown into the 

 synonymy within recent years, not only in America but also 

 especially in Europe. No doubt some of these belong there, but 

 it is very probable that many might be profitably employed for 

 the recognition of localized and various transitional forms 

 among these highly versatile flies. 



The foregoing remarks at least throw some light on what 

 may be termed the species-status in nature, and it is believed 

 that they demonstrate the need of a modified species-concept 

 for application in young stocks. It will be useful to summarize 

 the main points. 



SUMMARY. 



1. In old stocks, species have normal values and well defined 

 limits, because evolution has become inactive in those stocks 

 and maturity has been attained by the forms. 



2. In young stocks, the contraction of taxonomic values due 

 to youth restricts the scope of species, and the presence of 

 many transitionals due to active evolution obscures their limits. 



3. Therefore the species-status is not uniform in old and 

 young stocks, and the species-concept must be modified to 

 agree with it. 



