REVISION OF STREPSIPTERA PIERCE. 7 



Handlirsch (1903 an<l 1904) and Boernor (1904) have gone exten- 

 sively into the phylogeny of insects, and as a result of their work a 

 fifth rule may well be added to Kirby's: 



Rule V. When insects formerly placed arbitrarily in some of the older orders are found 

 by paleontology to be of a distinct line of descent from the order with which they have been 

 ranked, and show decided differences from this order in structure or in metamorphosis, 

 they should be separated out to form a new order. 



In converse also: Inserts which should be separated from an older order in accordance 

 ivith any of the preceding rules, and yet which show a common origin, must also constitute 

 a separate order. 



Mengea tertiarid, the only fossil insect yet found in'the Strepsiptera, 

 shows a nearer approach to other orders than any existent forms 

 except the very recently discovered Trioxocera mexicana, in that the 

 tarsi are five-jointed and two-clawed, but in other respects its char- 

 acters are essentially different from those of any contemporary group, 

 and indicate that the Strepsiptera have completely separated from 

 whatever lineage they formerly belonged to. 



Besides being isolated from all other orders by their morphology, 

 and by phylogeny, they may also be shown to be separated by the 

 anatomy of the alimentary, nervous, and reproductive systems at 

 least, by their embryogeny, and by their biology (metamorphosis and 

 reproduction). 



Following may be considered some of the principal characteristics 

 of the group upon which authors have based their conclusions that 

 it is worthy of a distinct ordinal name. The authority for each point 

 and the species studied are placed in parenthesis. 



1. The order became separated from its nearest related group in 

 or before the Tertiary age (Pierce, Mengea tertiaria Menge). 



2. Absence of labrum in male and female; very feeble development 

 of maxillae in male and complete absence in female (Nassonow, 1892 el, 

 Xenos vesparum Rossi (rossii Kirby). 



3. Position of mouth opening (referring to the constricted part of 

 the pharynx of the male) in the male and female at comparatively 

 considerable distances from the mouth parts (Xassonow, 1892 d, Xenos 

 vesparum Rossi). (See pi. 5, fig. 11.) 



4. Antenna! surface covered with an immense number of elevated 

 sensory organs (Pierce, Crawfordia pulvinipes, Acroschismus pallidus, 

 pecosensis, bowditchi, hubbardi). 



5. Modification of anterior wings of males into club-like balancers 

 (Nassonow, 1892 el). (See pi. 6, fig 7.) 



6. Reduction of prothorax, sometimes to a mere cylinder sur- 

 rounded by the mesothorax (Pierce, AntJiericomma barberi). (See 

 pi. 14, fig. 5.) 



7. Unusual development of metathorax and the great distance 

 between the last two pairs of legs. (See pi. 6, fig. 6.) 



