PARKKH: .\i:\\ i:X( ;i,A.\l) SAKCOI'lIAdlDAH. 27 
For (hied specimens wliieli h;i\i' to he relaxed, twelve to twenty- 
four hours (sometimes several days are necessary) in a moist chamljer 
will usually soften them sufficiently to make the parts Hexihie. Species 
with hlack genitalia seem to relax much (juicker than those with ' red.' 
The most satisfactory method for treating both dry and freshly 
caught material, the former having been relaxed, is as follows. Two 
pieces of sheet or pressed cork are taken about four inches long, one 
about an inch wide, the other two inches and a half. The narrower 
piece is fastened on top of the larger so that each has a long side flush 
with a long side of the other. The end view appears like two steps. 
Specimens are pinned into the part of the narrower piece that corre- 
sponds to the 'rise.' The pin is deeply inserted and both it and the 
longitudinal axis of the fly are parallel to the ' tread.' The remainder 
of the work is done most advantageously w^ith a binocular. A pin 
is taken in the left hand and held or pinned against the posterior 
dorsal surface of the abdomen to keep it steady. With the right hand 
another pin is inserted in front of the forceps and this is pulled or ratiier 
pushed backward and slightly upward. The result should be an 
'unrolling' of the segments. Sometimes they can be pulled so far out 
that no part is concealed within the abdomen proper and in such cases 
the fourth ventral plate is often completely exposed. When the seg- 
ments have been pulled out into the proper position the pin which is 
held before the forceps has only to be pushed down into the cork to 
hold them in place while they dry. Another pin inserted in front of 
the penis will keep the latter in its proper relation to the other parts. 
Probably a person working with genitalia will prefer to develop his 
ovm technique, but the above method may l)e suggestive. Species of 
Blaesoxipha, Agria, and other genera that have a very small second 
genital segment are less satisfactory to work with than those which 
have both segments of about the same size, the membranous connec- 
tions being less extensive and sometimes partially chitinized. In 
certain species of Sarcophaga the sixth segment is quite well developed 
and these species are hard to work with on this account. 
Measurements. 
Expressions of relative width, height, and length, as herein em- 
ployed, compare in ratio form the number of spaces of an eye-piece 
micrometer represented. They cannot be judged by the unaided eye 
with any great degree of accuracy. 
