Group Aphidina, Family Aphididae 7?i 



excentric. Two divisions or subtribes may be distinguished, the Macro- 

 ■siphii and Pentalonii. 



KEY TO THE SI^BTRIBES OF THE MACROSirHINI 



1. Venation normal; cornicles cylindrical or swollen, and nsnally witli closed 

 reticulations on the apical part; spuria usually with seusoria on" the third an 

 tennal segment MACUOSIPHII 



2. Venation reduced, abnormal or excentric: cornicles also show a tendency to 

 lose their distinctive Macrosiphini characters PENTALONII 



\\'hat was said about the swollen cornicles under the Aphidini 

 also holds true here. The Macrosiphii and Pentalonii undoubtedly 

 represent two distinct lines and are good subtribes, while Amphoro- 

 phora and related genera would seem to indicate a third line, which it 

 does not prove to be; at most it is a section under the ^lacrosiphii. 



The tribes Aphidini and Macrosiphini give us two of the largest 

 genera of the family. From the old genus Aphis we have carved genus 

 upon genus for nearly a century and attempts are still made to carve 

 additional genera out of it. It appears that we have about come to 

 the limit, as some of the later attempts are plainly artificial. Consid- 

 ering the relative length of the cornicles and cauda will, to be sure, 

 give us genera, arbitrary and artificial genera but not genera as found 

 in nature. The genus Aphis even as it stands today is too large and 

 unwieldly, and reduction would be desirable. A number of small, abor- 

 tive, genera will no doubt continue to be separated ofif. similar to 

 Toxoptera, Mastopoda, and Hysteroneura, but attempts to break up 

 the genus as a whole can not be made without destroying the generic 

 conception or resorting to artificial divisions. Large genera are not 

 uncommon and are to be found in most of the large familie-; ot plants 

 as well IS of animals, and the .Vphididae can now be considered as 

 a large family, llie two comparatively modern genera. Aphis and 

 Macrosiphum, are the ones in which the rate of evolution has reached 

 its maximum, and thev have become rich in species above comparison 

 and contain the principal progressive parts of the family. 



A great deal of attention has been given of late to the question 

 of types. Some of the more recent contributions would seem to imply 

 that this is the main purpose and aim of taxonomy, and with the set- 

 ting of a type we have the genus once for all fixed and it can not 

 again be changed. There are three kinds of types recognized by 

 phylogenists, which may be termed the chronological type, the phy- 

 logenetic type, and the biological type. The chronological type is the 

 one in vogue at present. It is usually the oldest species included in 

 the genus, or any species that happens to be considered as type by the 

 author of the genus. Two or more different types may be set for a 



