1938] 
Lines of Descent of Insects 
167 
lis has preserved the primitive archicephalic or supraman- 
dibular suture, characteristic of such Crustacea as Branchip- 
pus, Anaspides, etc. (9) The huge flagelliform antennae of 
Machilis are the most like those of trilobites and other primi- 
tive arthropods. (10) The huge monocondylar mandibles 
of Machilis are better developed and are more Crustaceoid 
(with separate incisor and elongated molar regions) than 
the reduced and highly specialized mandibles of the Dicellura 
and Protura. (11) The well developed paragnaths (super- 
linguae) of Machilis are larger and more Crustaceoid than 
those of other Apterygota. (12) The well developed maxillae 
of Machilis, with their huge limb-like palpi, are far more 
primitive than those of any other insects. (13) The 
lacinial fringes of Machilis are more primitively Crustaceoid 
than those of other insects. (14) The labial palpi etc., of 
Machilis are better developed, and are of a more primitive 
character than those of other Apterygotan insects. (15) 
The traces of the second maxillae forming the under lip are 
more distinct in Machilis than in other Apterygota. (16) 
The head of Machilis is of the ectognathous type, and is 
much more primitive than the entognathous type (with 
overgrown mouthparts) found in the Dicellura and Pro- 
tura, etc. 
There are many more features which might be cited to 
prove that Machilis is more primitive or “ancestral” than 
any other insect, but the facts cited above should be suffi- 
cient to convince any impartial investigator that Machilis 
is the most ancestral of all insects. Furthermore, its numer- 
ous unmistakably Crustaceoid features clearly prove that 
Machilis, and the other primitive insects descended from 
similar ancestors, were derived from Crustacea resembling 
the “Prototanaidacea” in many respects. The well known 
fact that many Apterygota exhibit striking similarities to 
various types of “myriopods,” merely indicates that both 
insects and “myriopods” were ultimately descended from 
the same (Crustacean) ancestry — and the Crustacea are 
the only intermediate forms serving to connect the insects 
and “myriopods” with the trilobites and other primitive 
forms at the base of the common arthropodan stem. 
If the Machilidse are the most primitive or “ancestral” 
insects, it is obviously misleading to insist that the Dicellura 
