INTRODUCTION 33 
Intrapostocular cilia are minute setae placed in a more or 
less well-defined row immediately behind the rear margin of the 
eye and in front of the first row of postocular cilia. This is a 
new term. The small setae are often difficult to discern and can 
be seen to best advantage only under high magnification and with 
good illumination. The row is most obvious in Callitroga and 
Paralucilia, less so in Onesia, Acrophaga, and Melanodexia. 
Proportional and dimensional characters were made with the 
aid of a cross-line dise placed between the lenses of the ocular 
in the binocular microscope. (The measurements given in this 
paper were secured with medium high power, and the same 
magnification was used throughout. ) 
Measurements are given in micrometer units instead of in 
millimeters. These measurements were secured by averaging 
the actual measurements in a series of specimens. The figures 
therefore represent relative and not actual lengths and widths. 
They are to be used as a basis of comparison between parts of the 
same specimen or as a basis of comparison between different 
species. Obviously, actual measurements of parts in individual 
specimens are of only minor importance. Extremes may be of 
great value in the future when series of specimens of the same 
species have been reared or collected, but for several of the 
species only single specimens have been available. 
Proportional measurements in specimens of the same species 
remain nearly constant. Those given may vary only as much as 
one-half unit in one direction or the other. Where greater differ- 
enees occur in series considered to be a single species, the 
instances are discussed in the text. In several cases where the 
character seems to lose its specific value, it is possible that more 
than one species exists in the series, or that the species is hetero- 
zygous for the character. There is the possibility that too many 
forms will be recognized as distinct species when reliance is 
placed on differences in measurements, but usually other charac- 
ters have been discovered to support the conclusions based on 
such measurements. 
Characters of this sort may be confusing at first to students 
not familiar with them, but a little practice will show that 
such differences may be as easily observed as others. It has 
been found that they may be trusted to show real specific 
distinctions more accurately than many other characters. 
Ten specimens of each sex were measured when this number 
was available, including the largest and smallest individuals, 
specimens from the extremes of the distribution, and several of 
average size. 
