306 ENTOMOLOGICAL NEWS. [July, 'l6 



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 Proturadclphia 

 (or Proturan brotherhood) comprising such insects as the 

 Eosentomidae, Acerentomidae, Neelidae, Sminthuridae> Acho- 

 rutidae, Entomobryidae, etc.; the Rhabdnradclphia (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 insect^s 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, Anaspidcs, etc.) and "Myriopoda" (e. g., 

 Scolopcndrella, 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 Nathorslia approach rather closely to the lines 



