No. 625] THE EVOLUTION OF ARTHROPODS 



161 



of the ancestors of insects and their relatives has been 

 the attempt to derive them all from one type of creature 

 — which is manifestly impossible, since even the lowest 

 representatives of any group dii¥er markedly among 

 themselves, and their ancestors also must have differed 

 markedly among themselves (although not to such a 

 great extent as their progeny do). 



Although such Anomostraca as Batliyndla have be- 

 come specialized along their own lines of development, 

 they have retained many features which suggest what 

 some of the ancestors of the insects and Symphyla must 

 have been like, and I think it very probable that the an- 

 cestors of ScolopeiidreUa and the Protura were quite 

 similar in many respects to Bathynella, while other ap- 

 terygotan insects, such as Macliilis, have carried over 

 more characters from the tanaidacean side of their com- 

 mon ancestry. Therefore, if we accept the idea that 

 some of the common ancestors of insects, isopods and 

 Symphyla occupied a position intermediate between the 

 lines of development of the Anomostraca and the Cu- 

 macea-Tanaidacea, and differed n little less among tliem- 

 selves than the Aiiomostrncn do from tlio ( 'nmac(>a- 

 Tanaidacea, it bocoiiics lici-l'-'ctly dc;))- llint >(»iiic nptrry- 

 gotan insects could Inlirrlt IVom \\w t;in;n.l:iccMM side of 

 their common ancestry cliai'Mrtci's wliicii aNo M]»]K'nr in 

 the isoi)ods which ai-e dcriNcd fi'diii 'raiinidacca iikr foi-e- 

 bears; while on the oIIut liaiid. otli.-r aptn-N i^otan iiiMM-r^ 

 could inherit from tlic h'ulhinn /hi si.lr ot' liirii' (•(.miiion 

 ancestrv certain cliai-actci's wliidi aNo apjicar in the 

 Symphyla or other r..rni^ .]<-.M.n.hMl iVoni /lafln/nrlla- 

 like forebears. 



The Protura (such a^ A' < i > ^.in.nn,^, Kn^, ntnnn,u . vX^-.) 

 are the most primiti^•t' i-cprr-t'nlat i\cs of liic lii-ccta, 

 and have inherited lV(»ni llicir cniiinuui aiicr-tr> many 

 features also preserve! in the " ^[yri(»|)(Mla " ; and the 



wliich Ihrv h.-loii- ha'^ niurh in connnon with that of the 

 "M.M-i..lKMhi/' a. ha^ iKvn pointed out hN I>hiliptM-henko, 



