1899] ENTOMOLOGICAL NEWS. 91 



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specimens of these species. To me the vertex appears sub- 

 angulate and the other characters those of group II. Even 

 superficially they show a far closer relationship with the spe- 

 cies cited under group II than with smavafjdida and its allies. 



In a study of the characters of Empoanca it is an exceedingly 

 difficult matter to eliminate all possibilities of error in observa- 

 tion. Possible errors may be attributed to two causes, (1) 

 malformation produced by drying, and (2) optical illusions 

 due to varying position of parts. 



Among the Typhlocybids we find insects almost as delicate 

 and frail as some of the Capsids. The great delicacy of the 

 body walls renders the proper preparation of specimens a very 

 difficult matter. When mature specimens are selected and 

 prepared with great care, the distortion caused by drying is 

 reduced to a minimum ; but as in the case of Aphida and the 

 little yellow and green culicid-like flies that fly about our 

 lamps, an examination of fresh, undried material is almost 

 imperative. I know from observation that drying produces 

 marked changes in the form of vertex and face, and the usual 

 collapsing of the abdomen throws the genital organs out of 

 their natural position. 



With the parts thus distorted errors are still more likely to 

 occur in viewing various details under the microscope. Even 

 under ordinary circumstances there is the widest chance 

 for error (and this is true of many other Homoptera) . In fo- 

 cusing a half or two-thirds objective on a convex vertex the 

 proper reading of the width can be readily made, but a very 

 slight change in the angle of the long axis of the body or in 

 the focusing will produce differences of specific or even sec- 

 tional value. The same is true of the face. Unless the point 

 of the vertex and the tip of the clypeus are equidistant from 

 the lens, an error in the reading of the lens will surely be 

 made. 



No part is more difficult to study than the last ventral seg- 

 ment. Collapse of the abdomen frequently throws it out 

 almost perpendicular to the body axis. It assumes something 

 of'this form when the 'ovipositor is in use. There is but one 

 accurate point of view, and this is obtained when the base of 

 the segment and its apex are equi- distant from the lens. This 

 is a view rarely obtainable on the specimen as ordinarily 



