36 PROC. ENT. SOC. WASH., VOL. 23, NO. 2, FEB., 1921 



lines of descent drawn as though springing from such a point of 

 origin would form a cone-like figure, solid at its base (where many 

 annectant forms connect the various lines of development in all 

 directions), but gradually splitting up into distinct lines of 

 development as the connecting forms are lost. Some of these 

 lines of descent parallel each other quite closely for a greater or 

 less extent of their course, while others diverge more markedly 

 as evolution progresses. 



While a diagram of the lines of descent of the insectan orders, 

 such as that described above, would represent the actual inter- 

 relationships of the orders much more accurately, there is great 

 danger of making the figure so intricate that it is incompre- 

 hensible to any one save its author, thereby defeating its main 

 purpose, which is to aid in visualizing the interrelationships and 

 points of convergence of the lines of descent in question. I 

 have therefore represented the lines of descent of the insects 

 grouped about the Neuroptera (;'. e., those of the Diptera, 

 Mecoptera, Trichoptera, Lepidoptera, Neuroptera, etc.) by a 

 single line in the appended diagram, and I have used only the 

 Neuroptera, with their immediate relatives the Mecoptera, to 

 typify these lines of descent, since the Neuroptera and Mecop- 

 tera are the most important representatives of the group, and 

 have retained many features exhibited by the other forms as 

 well. 



In this connection, it should be noted that although the 

 Hymenoptera are represented in the diagram as a little lower 

 down than the Neuroptera and Psocida, this fact has no phylo- 

 genetic significance, since the three lines originate at about the 

 same level, and the Psocida (and probably the Neuroptera also) 

 are if anything a little more primitive than the Hymenoptera 

 are. On the other hand, the Mallophaga, Pediculidae, etc., 

 which are descended from Psocida-like forebears advance much 

 further along the road to morphological specialization than the 

 Hymenoptera do, and similarly the higher Diptera, etc., which 

 are descended from Neuroptera-like forebears, likewise travel 

 further than the Hymenoptera do along the road to morpholo- 

 gical specialization, so that it has seemed preferable to draw 

 these two lines of descent somewhat longer that that of the 

 Hymenoptera, in the diagram. 



With regard to the often debated question as to which order 

 of insects is the "highest," it would seem to the disinterested 

 observer that such arguments are quite pointless unless one 

 considers the order as a whole, and takes into consideration the 

 character of its most primitive representatives, rather than the 

 degree of specialization of its most modified representatives. 

 Thus for example, the Crustacean Sacculina is much "higher' 

 or more specialized than any known insect, yet no one would 

 argue from this that the Crustacea are "higher" than the Dip- 



