﻿STINK BUGS, GENUS MECIDEA — SAILER 477 



cerning animal dispersal and zoogcographical relationships. 



Bibliographic references to literature concerned with the distribu- 

 tion of the group discussed in this paper may be found on page 503. 



CHARACTERS USED FOR SEPARATION OF SPECIES 



In general appearance the species of Mecidea are very similar 

 (see fig. 89.) They are unusually uniform in size and color, and such 

 differences as do exist can be expressed only as averages. These 

 differences are often as pronounced within species as between species 

 and so have little value for purposes of identification. The characters 

 seeming to have importance for purposes of specific differentiation are 

 those associated with the internal male genitalia, the shape of the 

 pronotum, and with the antennae of both sexes. These characters 

 are relatively stable but are not easy to use. The antennae show such 

 marked sexual dimorphism that the sexes of each species must be 

 treated individually, while examination and comparison of the internal 

 male genitalia involve rather complicated dissection and preparatory 

 technique. 



A step-by-step outline of the technique utilized for study of the 

 internal male genitalia follows : 



1. Relax specimen. A solution of one-third 95-percent alcohol, 

 one-third ethyl acetate, and one-third water has proved very effective, 



2. Detach genital segment from the abdomen and place the seg- 

 ment in a hot solution of 10 percent KOH. 



3. Remove the segment as soon as it turns dark brown and place 

 in water, 



4. By using two fine teasing needles, each having their points 

 slightly bent, withdraw the aedeagus either through the genital open- 

 ing or through the open posterior end of the genital segment. 



5. Once the aedeagus is free, osmotic pressure will cause the lateral 

 and median penial vesiculae to expand. The lateral vesiculae and 

 often the median vesicula expand to maximum size without further 

 trouble. If the median vesicula fails to escape from its invaginated 

 position above the penisfilum, manipulation and pressure applied to 

 the cylinder of the aedeagus mil usually force it out, whereupon it 

 will expand in a normal manner. Caution: Care must be exercised 

 not to puncture either the walls of the lobes or of the cylinder of the 

 aedeagus, as this results in the immediate collapse of the vesiculae. 



6. After study of a specimen is finished the genital segment and 

 the aedeagus may be placed in a small (10X4 mm.) vial containing 

 a drop of glycerine. The vial may then be corked and attached to the 

 pin containing the corresponding insect. The vesiculae immediately 

 collapse when the aedaegus is placed in glycerine but will reexpand 

 readily when returned to water. 



