288 THE CANADIAN ENTOMOLOGIST 



may perhaps also be derived from arthropods similar to the 

 Apodidjc, or the Branchiopoda, but their line of development 

 leads through such forms as the Leptostraca (and their relatives), 

 to the Cumacea, Tanaidacea, and Anomostraca; while the line of 

 development of the arachnids leads from the Branchiopoda, or 

 Apodidee, through the trilobites to the Merostomata', Eurypterida, 

 etc., as can be readily seen by comparing such fossil merostomes 

 as Bunodes lunula and other antenna-bearing Merostomata, with 

 the Trilobita. 



I would, therefore, maintain the following points: 1. That 

 "the trilobites do not stand in the direct line of descent of insects, 

 but rather in a side branch leading ofif from the Branchiopoda 

 and Apodidse to the Merostomata, Eurypterida, and other arach- 

 noid forms. 2. That the line of development of insects leads 

 from the branchiopod (and apodid) type of arthropod, through 

 such forms as the Leptostraca and their relatives, to the Anomo- 

 straca, Tenaidacea, and other crustacean forms which have 

 preserved many features characteristic of the ancestors of insects 

 and "myriopods". 3. That the members of the Symphyla- 

 Pauropoda group are in many respects quite similar to certain 

 of the ancestors of the "myriopods" in general, and that the mem- 

 bers of the Symphyla-Pauropoda group are likewise very similar 

 to certain ancestral insects, whose line of development is quite 

 closely paralleled by that of the "myriopods" in question. 4. 

 That the Apterygota in general have departed the least from the 

 ancestral condition of insects as a whole, and the Protura are as 

 primitive as any known Apterygota. 5. That apterygotan forms 

 such as the Lepismids, etc., are very like the ancestors of winged 

 insects and are structurally very closely related to the ephemerids 

 and Plecoptera, which, with the fossil Palaeodictyoptera, are the 

 most primitive representatives of the pterygotan group. The 

 details of the discussion of the evolution of insects, together with 

 the grouping of the orders into super-orders containing the forms 

 which are anatomically the most closely related, will be taken up 

 more. at length in a later paper dealing with the latter phase of 

 the subiect. 



Mailed August 24th, 1918. 



