118 Psyche [October 



were derived from the fossil Protodonata, and the hnes of develop- 

 ment of these forms were therefore placed close together in the dia- 

 gram. The Odonata are apparently fairly closely related to the 

 Ephemerida, but their line of development leads away from that of 

 most of the other insects, and they are such highly aberrant forms 

 that a study of their anatomical features is of but little value in 

 attempting to trace the lines of descent of winged insects in general. 



COLSOPTERA 



\ DERMAPTER/l 



\ \ EMBIIDINA 

 \\ HADENTOMOIDA 



\\ / ^PLECOPTERA 

 \\ / /^HAPLOPTEROIDA 



Fig. 2. Lines of descent of the Panplecoptera. 



In Fig. 2, the lines of descent of the insects comprising the super- 

 order Panplecoptera {i. e., the Haplopteroida [fossil], Plecoptera, 

 Hadentomoida [fossil] Embiidina, Dermaptera, Hemimeridse, etc., 

 and possibly including the Coleoptera as well) are shown. If we 

 take into consideration only the Plecoptera, Embiidina, and Der- 

 maptera, the group is characterized in general by a tendency to- 

 ward the prognathous type of head {i. e., mouthparts directed 

 forward), the presence of three segments in the tarsi, and the ab- 

 sence of styli on the posterior margin of the hypandrium, or sternal 

 plate beneath the genitalia of the male insect. The mesothoracic 

 coxse are usually as broad, or broader than long in these insects, 

 and there is a marked tendency toward the retention of the longi- 

 tudinal, rather than the cross veins of the wing in the members of 

 the group . 



Handlirsch states that the fossil Haplopteroida are closely re- 

 lated to the Plecoptera and that the fossil Hadentomoida are 

 closely related to the Embiidina, so that the lines of descent of 

 these forms have been represented as though extending rather close 

 together in the diagram. The Haplopteroida are in some respects 

 more specialized than the Plecoptera, and their line of descent 



