A COMPARATIVE STUDY OF THE EXTER- 

 NAL ANATOMY OF PLANT LICE. 



BV R. A. VICKERY^ jNl. A. 

 Assistant in Entomological Division of Minnesota Kxperinient Station. 



The following article by Air. \'ickery represents a thesis prepared 

 for the degree of M. A. at the University of Alinnesota. The work 

 was begun, and with the exception of a few additions, and some re- 

 vision, made in our laboratories, practically completed under the direc- 

 tion of Prof. O. W. Oesthmd, to whom the author is particularly 

 indebted for guidance and encouragement. 



The object of the investigations reported upon was to name and 

 classify some of the external characters of the Aphidid?e in such a way 

 that systematic work in this group could be made easier and more ac- 

 curate. 



To present the subject in complete form the author has been 

 obliged in a few instances to incorporate in the body of the text some 

 well known facts and already recognized terms, but this in no way de- 

 tracts from the originality of the work as a whole, and I believe he has 

 added materially to our working knowledge of plant lice. — F. L. W. 



In many of the published descriptions of plant lice it is impos-sible 

 to make more than a guess as to what species the author is describing. 

 Generic and even family characters have been used in specific descrip- 

 tions. In the work upon which this paper is based about one hundred 

 species represented by large numbers of individuals in different stages, 

 were studied with 2-3* and 1-6 objectives. Particular attention was 

 given to the antennae, wings, cornicles and cauda, as these organs 

 afford some of the best characters, and the rostrum, hind legs, anal 

 plate and genital plate also afford good characters. These points have 

 been illustrated by plain line text figures, as such figures are easier to 

 use, and show the points just as well as the more elaborate plates. 



The presence or absence of certain organs, such as the lateral 

 tubercles, or certain sensoria of the antennre cannot be used in spe- 

 cific descriptions ; but the arrangement or character of these organs 

 may be so used. Describers of species pay too little attention to minute 

 characters. Published figures accompanying descriptions should con- 

 tain detailed drawings of the important organs. This method would 

 advance our knowledge of the value and constancy of certain charac- 

 ters, and make it possible finally to make up practical keys to the 

 genera and species of the Aphidid:e. It is hoped that this paper will 

 helj) in some degree toward tliat end. 



