N0.1438. WINGS OF THE TENTHREDINOIDEA—MacOILLIVRAY. TilS 



front margin of the wing of Midas as compared with that of Pantarhes 

 or Era.v (tig. 22), Midas showing the highest type of efficiency, a 

 long, narrow triangle. 



VI.— THE PHYLOGENY OF THE TENTHREDINOIDEA. 



It is essential in determining the phylogeny of any group to ascer- 

 tain what are the most primitive forms, to compare them, and to 

 determine the ways in which they have been modified. In making 

 these comparisons the structure of a set of organs should be studied 

 and the phA'logeny of the group determined from this study; then 

 other sets of organs should be examined, until all the organs of the 

 animal have been examined, phylogenies based on these studies should 

 be made, and then compared with the phylogeny hrst determined. If 

 it is found that these successive phylogenies corroborate each other, 

 we have a demonstration of the correctness of our conclusions. If 

 they disagree, then there is indicated a need for a further examination 

 of the disagreeing forms, for when correctl}" interpreted it will be 

 found that the ditierent records of the action of natural selection will 

 not contradict but confirm each other. In the following pages the 

 first step in such an investigation, a phylogen}^ based on an examina- 

 tion of the wings of the Tenthredinoidea, is given. 



There arises, in" working out the phjdogeny of any group, the ne- 

 cessity for distinguishing between different kinds of characters. 



First, characters indicating difference in kind of specialization; and second, charac- 

 ters indicating difference in degree of specialization of the same kind. The former will 

 in<Ucate dichotomons divisions of lines of descent; the latter merely iiuhcate degrees 

 of divergence from a primitive type. Thns, it is shown that there are two distinct 

 ways of uniting the two wings of each side in the Lepidoptera; they may be united 

 by a frenulum, or they may be united by a jugum. These are differences in kind of 

 specilization, and indicate two distinct lines of descent or a dicliotomous division of 

 the order. Among those Lepidoptera in which the wings are united by a frenulum 

 great differences occur in the degree to which this organ, or a substitute for it, is 

 developed; such differences may merely indicate the degree of divergence from a 

 primitive type, and may need to be correlated with other characters to indicate 

 dicliotomous divisions." 



There is also a necessity, as is shown by Comstock, to distinguish 

 betw^een the characters used by systematists merely to make it possi- 

 ble for students to recognize the members of a group — reaH/jiifio/i 

 characters and the essential cJiaracters of a group. The essential 

 characters of a group are not necessarily dependent on the presence 

 or absence of any character or in the form of an}' part of the l>od3', 

 but on the characteristic structure of the progenitor of the group and 

 the direction in which the descendants of this progenitor have been 

 specialized. Recognition characters are generall}' those first observed 

 and used by the systematist. They may also be essential characters, 



« J. H. Comstock. Evolution and Taxonomy, Wilder Quarter Century Book, p. 42. 



