Dec, i9i6.] Relationships of Apterygotan Insects. 28L 



scaled. Abdomen apparently composed of ten segments, the tenth 

 and eleventh being more or less closely united. First abdominal 

 segment with two submedian hairy papillae, and also bearing a pair 

 of short stout spine-like styli (unlike the rather long slender styli 

 of the Projapygidse) which likewise occur on segments two to seven 

 inclusive. The cerci are represented by imperforate forceps-like 

 terminal appendages. Anal laminae not distinct in adults. Eight 

 abdominal ganglia. Seven pairs of spiracles in abdominal region. 

 Malpighian tubules wanting. Seven ovarioles present. Foregut ex- 

 tending posteriorly only to metathorax (not to fifth abdominal seg- 

 ment as in Projapygidse). This order contains the family Japygidse 

 (to which may be added the Projapygidse, if the latter are not to be 

 regarded as representing a distinct group). 



The Campodeidse are more primitive than the Japygidae, although 

 they are apparently not much (if any) more primitive than the Pro- 

 japygidse. The Projapygidse, as was mentioned above, occupy a posi- 

 tion intermediate between the Japygidas and Campodeidae. They are 

 regarded by some investigators as the lowest of living insects but the 

 Protura are more primitive in many respects (although they have 

 become strongly modified in certain structural details). The Cam- 

 podeidae and Projapygidse may possibly be regarded as occupying a 

 position somewhat intermediate between the Protura and the next 

 group to be considered. 



III. Section Thysanuradelphia. 



7. Dasyleptoides (Mononemura). — This group comprises the 

 family Dasyleptidse founded on the fossil insect Dasyleptus lucasi, 

 described by Brongniart as follows. Body cylindrical, tapering 

 posteriorly, and terminated by a single multiarticulate filament, which 

 is as long as the body. Antennse and legs robust. Head quite large. 

 Prothorax very short, and meso- and metathorax, which are of equal 

 size, much longer than the prothorax. Abdominal segments ten in 

 number, and equal in size; the last, which bears a multi-articulate 

 filament, a little longer than the others. Some specimens appear to 

 have abdominal plates similar to those found in Machilis. The en- 

 tire body (antennae, legs, thorax and abdomen) covered with numer- 

 ous very short hairs. The body, including the terminal abdominal 



