66 Eighteenth Report State Entomologist of Minnesota — 1920 



greatly from the time of its first recognition by Koch to the 

 present. Koch's conception of the tribe inchided the Chaitophor- 

 ina and the Macrosipliini. Passerini (1863) submerged the trilxil 

 conception and erected the subfamily Aphidinae of much wider 

 extent that that of Koch's tribe. Buckton (1876) uses the sub- 

 family term of Passerini in a tribal sense. Thomas (1878) first 

 used the tribal term Aphidini but included the Chaitophorina and 

 Callipterina. Oestlund (1887) excluded the Chaitophorina and 

 Callipterina, in which sense Wilson (1910) also makes use of the 

 term. Van der (lOot (1913) gives the trilje under the term 

 Siphonophorina, including also the Myzini and Macrosiphini. 

 Baker (1920) reduces the tribe to a subtribe under the term 

 Aphidina. 



A tribe is a group of genera that can be traced from a common 

 origin and which have certain characters in common. Tribes are not 

 arbitrary divisions, but are the expression of phylogenetic relationship 

 of a higher order and wider extent than those of genera. They will 

 appear from e.xtended biological and anatomical studies. Tribes are 

 not safely established on too limited or arbitrarily chosen characters, 

 but their test comes with the application of a number of additional 

 characters which will build up into a harmonious whole. Tribes are 

 also expressions of distinct lines of development separating them from 

 other lines or tribes. Such lines may also run through two or more 

 tribes expressing a still higher relationship. We have two such greater 

 lines within the subfamily Aphidinae. which stand out sharply when 

 attention once is directed to them. The two lines may be termed the 

 Pterocommini-Aphidini line and the Calaphidini-Myzini line, and 

 closely associated with the second the Calaphidini-Macrosiphini line. 

 The two lines may also be distinguished as the small and large race: 

 the first with shorter body, more rounded or abruptly pointed posteri- 

 orly; shorter antennae and legs. The second is of larger size but of 

 more slender body-form and gradually pointed posteriorly ; the anten- 

 nae and legs are usually very long in comparison. This is a curious 

 fact, but runs more or less distinctly through the whole family. Anal- 

 ogous conditions are not rare in other groups of animals. Some of 

 the more conspicuous morphological characters besides those just 

 mentioned are the conspicuous presence of lateral tubercles in the 

 first line, while the same are usually inconspicuous or absent in the 

 second line. Attention has often been called to these structures by 

 investigators of the family, from the time of Kaltenbach to the pres- 

 ent. Van der Goot has lately used them as generic characters in his at- 



