306 ENTOMOLOGICAL NEWS. [July, 16 
sections seem almost as distinct as these two, so that tempo- 
rarily, at least, I would regard all five sections as representing 
distinct limbs of the developmental tree, two of which exceed 
the others in size and importance. 
Among the Apterygotan forms there are but three sections 
—which also represent the main evolutionary lines of develop- 
ment in these insects. These sections are the Proturadelphia 
(or Proturan brotherhood) comprising such insects as the 
Eosentomidae, Acerentomidae, Neelidae, Sminthuridae, Acho- 
rutidae, Entomobryidae, etc.; the Rhabduradelphia (or Rhab- 
duran brotherhood) comprising the Rhabdura, Dicellura, etc., 
and the Thysanuradelphia (or Thysanuran brotherhood) com- 
prising such forms as the Lepismidae, Machilidae, etc., and 
about these three nuclei all of the wingless insects group them- 
selves. 
The Thysanuran line of development appears to approach 
as closely as any to that of the lower winged forms, but the 
retention of many of the characters found in certain wingless 
forms, by certain of the lower winged insects, makes it rather 
difficult to determine the exact relationships of the different 
lines of descent; and it is very probable that no one group of 
Apterygotan insects occupies the position of “mediary” be- 
tween the wingless and winged forms, but the winged forms 
probably approach all of the Apterygotan groups to some ex- 
tent, or arose from ancestors combining characters common 
to a number of Apterygotan groups, and therefore occupying 
a position somewhat intermediate between the groups in 
question. 
The lines of development of the Crustacea (e. g., Bathy- 
nella, Koonunga, Anaspides, etc.) and “Myriopoda” (e. g., 
Scolopendrella, etc.) very closely parallel those of the lower 
insects, such as Eosentomon, Anajapyx, Machilis, etc., so that 
the Crustacea, “Myriopoda” and Insecta may be regarded as 
forming the three apices of a triangle, each apex of which is 
connected with the other two by mutual bonds of relationship. 
The lines of development of such Trilobites as Triarthrus, 
Neolenus and Nathorstia approach rather closely to the lines 
