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Psyche 
[December 
(such as Campodea, Anctjapyx, etc.) are the most ancestral 
insects, since they are much more specialized than the 
Machilidse. In fact, the Dicellura could readily be derived 
from a slender blind Nicoletia type of Lepismatid Tysanu- 
roid insect (descended from Machilis like forebears) but 
by no stretch of the imagination could the primitive Machilis 
type of insect be derived from any Dicelluran type — which 
should be the case if the Dicellura represent the ancestral 
insects (leading back to some type of “myriopod”) . 
Because they have mouthparts of the concealed type, the 
Dicellura are sometimes grouped with the Collembola (and 
Protura) in the division Endognatha, in contradistinction 
to the Ectognatha, or Thysanuroid forms with mouthparts 
of the exposed type. The modifications of the mouthparts 
of the Dicellura, however, are not very similar to the modi- 
fications exhibited by the Collembola and Protura; and the 
Dicellura are only very distantly related to the other 
“endognathous” Apterygota, while the occurrence of cerci, 
and styli-bearing coxites, in the Dicellura, allies them more 
closely with the Thysanuroid Apterygota. It is therefore 
preferable to unite the Dicellura with the Lepismatidse 
(Thysanura) and Machilidae (Protothysanura) in the sec- 
tion Styligera, characterized by the occurrence of styli- 
bearing coxites, and cerci, as opposed to the Astyligera 
(Collembola and Protura), in which these structures are 
lacking. The Dicellura were possibly derived from some 
Niceletia-\ike Lepismatid insect, and the Lepismatidse them- 
selves were apparently derived from ancestors closely allied 
to the Machilidae. The Lepismatidse, in turn, serve to con- 
nect the Machilis-\ike ancestors of the Apterygota with the 
ancestors of the Pterygota, which are best represented by 
“larval” Ephemerida (which have three caudal filaments 
like those of Thysanuroid Apterygota), so that the Lepis- 
matid line of development is an extremely important one 
for the study of the evolution of the higher insects. 
The Protura are the most primitive representatives of 
the section Astyligera, although they have lost the eyes and 
antennse, and their mouthparts are rather highly specialized. 
They differ from the rest of insects by the fact that they 
exhibit a postembryonic increase in the number of segments 
(they have nine abdominal segments as “larvae”, and eleven 
