1917] A Phylogenetic Study 343 



of the parts in question is necessary before this point can be 

 definitely determined but the "phylogenetic" evidence would 

 indicate that Peterson's interpretation of some of these struc- 

 tures may need revision. A detailed comparison of the mouth- 

 parts, accompanied by drawings of the insects in question, will 

 be published later, as a part of the series dealing with the 

 phylogeny of the Diptera, Mecoptera, etc., so that it is unneces- 

 sary here to do more than call attention to the tendency toward 

 an elongation of the mouthparts exhibited by certain Neuroptera 

 (Fig. 4), and developed to a greater extent in certain Mecoptera 

 (Fig. 5), while it is carried to an extreme in the Culicids and 

 other Diptera. 



A comparison of the heads of the larvas under consideration 

 has thus far been rather disappointing, due to the fact that it 

 is necessary to examine a far wider range of .forms than is at 

 present available, in order to select those which have preserved 

 the desired characters — and it is largely a matter of chance 

 whether one is so fortunate as to find these or not. I have no 

 Culicid or Chrysopid larvas at present, but I recall having 

 observed in them a "cervical plica, " or fold of the membranous 

 region of the neck, which projects over the head capsule for 

 a short distance and is attached to it at the point labeled "x" in 

 Fig. 10 of a Panorpid larva. In some of the Trichopterous 

 larv^ which I have examined, a similar "cervical plica" is 

 attached to either side of the head capsule, but it is not so well 

 developed in the Trichoptera. It is possible that a further 

 overgrowth of the head capsule by the neck-fold mentioned 

 above, has resulted in the condition exhibited by the Tipulid 

 larva shown in Fig. 13, in which a fold of the neck membrane 

 has grown over the head capsule, to which it is very closely 

 applied, as far forward as the line labeled "y" in Fig. 13. 



As far as the head region of the larvae is concerned, the 

 Diptera seem to be about as similar to the Neuroptera as they 

 are to the Panorpids, and the head of a larval Panorpid is 

 somewhat more " Neuropteron-like " than the head of a larval 

 Trichopteron is. In the case of the adult head, however, the 

 Diptera are closer to the Mecoptera than to the Neuroptera, and 

 also appear to be very much closer to the Mecoptera than to 

 the Trichoptera. In conjunction with the study of such other 

 features as the antennae, mouthparts, thoracic sclerites, legs. 



