6 PROCEEDINGS OF THE NATIONAL MUSEUM vol.71 



MEASUREMENTS 



Various comparative measurements of body parts have been used by 

 different describers of species. These are most often the compara- 

 tive length of the first two segments of the antennal filament, and the 

 length of the petiole as compared with that of the hind coxa and tro- 

 chanter taken together. 



Several thousand such measurements taken with a filar micrometer 

 indicate that while those of the antennal filament segments may, in 

 some cases, be of value, those of the petiole, as compared with the 

 hind coxa and trochanter, can not often be relied upon. 



To obtain such measurements accurately, the measuring limit points 

 must be accurately fixed. The petiole is usually measured from the 

 attachment of the levator muscle on it to the point where the dorsal 

 plate begins at its hinder end. With the coxa and trochanter, however, 

 no common points have been established and the irregular ends of 

 these segments, caused by the irregular sockets, make it impossible to 

 obtain really accurate figures. It is rare that coxa and trochanter are 

 in the same plane and the points of beginning and ending of the meas- 

 uring can not be made identical in many cases. Variation, too, is found 

 here. In one species the petiole varies, in proportion to the coxa plus 

 trochanter, from 0.62 to 0.89, and in specimens from the same State 

 between 0.63 and 0.77. Under the microscope the difficulty of placing 

 the piece to be measured, exactly at right angles to the line of vision, is 

 also met with. Repetitions of measurements of the same specimens have 

 given variations as great as 0.07, in spite of the utmost care to obtain 

 accuracy, and the final conclusion reached is that the only use which 

 can be made of such measurements is where the petiole is shorter 

 than, or at least no longer than the coxa, as compared with those 

 where it is at least as long as the coxa and half of the trochanter 

 taken together. 



COLORS AND COLOR VARIATIONS 



These may be perhaps most easily described on the unproved 

 assumption that the insects of this genus were originally entirely 

 black, and in a few species (as luduosa) this is still the case. Assum- 

 ing a tendency to the developing of ferruginous, this will first 

 appear on the second abdominal segment and on the middle of the 

 mandible, and its first evidence is a change to black with a reddish 

 tinge which may perhaps be termed piceous. Increase of the fer- 

 ruginous influence leads to dark red, then to ferruginous proper. As 

 this tendency increases, more abdominal segments become involved 

 until the entire abdomen is ferruginous and, in some cases, even pale 

 ferruginous. This color may spread forward as well as backward, 

 involving the first abdominal segment, but the petiole appears quite 

 resistant to this tendency, and the thoracic mass and head appear to 



