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Psyche 
[December 
poda”) and those of the ‘“Myriopoda” (represented in the 
diagram by the hypothetical “Protosymphyla” — which 
would include the direct ancestors of the Chilopoda, Pauro- 
poda, etc., as well as those of the Symphyla themselves). 
The hypothetical “Protapterygota,” or common ancestors 
of the Apterygota (and consequently the ultimate ancestors 
of the Pterygota also) , are best represented by the Machilis- 
like Apterygota, although some investigators insist that the 
Dicellura (such as Campodea, Anajapyx, Japyx, etc.), or 
the Protura, are the most primitive or most “ancestral” in- 
sects, despite the fact that the Machilis-\ike Apterygota are 
morphologically the most primitive (and hence the most 
“ancestral”) of all insects. Some of the features which 
indicate that Machilis (or the family Machilidse), rather 
than the Dicellura or other forms, represents the ancestral 
type better than any other living insect, is indicated by the 
following facts. (1) Machilis has more abdominal limbs 
(represented by eight pairs of distinct, styli-bearing cox- 
ites) than any other insect, including Campodea and other 
Dicellura. (2) The abdominal limbs, or coxites, of Machilis 
project free and distinct from the sternites (and the coxites 
of the ninth segment are hugely developed), while the 
abdominal limbs of the Dicellura, for example, are reduced 
to mere styli-bearing areas scarcely distinguishable from 
the abdominal sternites with which they have merged — and 
no other Apterygota have more than three pairs of abdomi- 
nal limbs. (3) The cerci, or limbs of the eleventh abdominal 
segment, are larger and better developed than those of any 
other insect. (4) The terminal abdominal segments of 
Machilis are more distinct, or less fused, than those of the 
Dicellura, for example. (5) The thoracic terga are better 
developed and overlap the lateral regions in a more primi- 
tive, or Crustaceoid fashion, in Machilis (and Lepisma ) , 
while in other Apterygota the thoracic terga are not of this 
type. (6) The thoracic limbs are best developed in Machilis, 
and bear styli (epipodites?) in the Machilidae alone. 
(7) Machilis has primitive compound eyes structurally simi- 
lar to those of Crustacea, and also has well developed ocelli 
(which likewise occur in certain trilobites, Anaspidacea, 
etc.), while the Dicellura are eyeless — as is also the case 
in the Protura (which likewise lack antennae) . (8) Machi- 
