1938 ] Lines of Descent of Insects 173 
quently bear mesal prongs, etc., in the members of this 
superorder. 
These insects are the more or less direct descendents of 
the Protorthoptera in the restricted sense ( i.e ., the Pro- 
torthopteran forms other than the Protoblattids) , and their 
most primitive representatives are the Grylloblattids, which 
are practically living Protorthoptera, closely related to the 
Stenopelmatoid Orthoptera (including the Gryllacris- types) . 
The latter are connected with the Grylloid Orthoptera by 
the Prophalangopsidse (and Tridactyloid types), and are 
connected with the Acridoidea by the Tettigoniidse (unless 
the Tridactyloidea furnish the intermediate forms leading 
to the Acridoidea). 
The Hemipteroid or Psocoid insects comprise the division 
Hemipteradelphia, or Parametabola, characterized by the 
development of a mesal detached lacinial structure forming 
a setiform, or a chisel-like portion of the maxilla (excepting 
the Zoraptera, which have a normal type of maxilla). The 
insects belonging to this division may be grouped into two 
superorders, namely the Panpsocoptera (Psocopteria) in- 
cluding the Psocoptera, Mallophaga and Anoplura, and the 
Panhemiptera (Hemipteria) including the Hemiptera and 
Thysanoptera. The lacinial structures are usually chisel- 
like in the members of the superorder Panpsocoptera, 
and are setiform in the members of the superorder 
Panhemiptera. 
The Zoraptera are the most primitive representatives of 
the Hemipteroid insects, and exhibit so many characters 
suggestive of a close relationship to the Isoptera, that this 
might be taken to indicate that they and the Hemipteroid 
insects in general were derived from the same Protorthop- 
teroid ancestry as the Isoptera were. On the other hand, 
the venation of the Zoraptera shows that they are members 
of the order Psocoptera, closely related to such Psocids as 
Archipsocus and Embidopsocus which exhibit some char- 
acters suggestive of a derivation from Embiid-like ances- 
tors; and the Psocoptera in general were probably derived 
from the common Protorthopteroid ancestors of the Isoptera 
and Embioptera. The Mallophaga are undoubtedly de- 
scended from ancestors extremely closely related to the 
Psocoptera, and may represent merely degenerate wingless 
