160 



THE AMEBIC AN NATURALIST [Vol. LIII 



near as any kti(»\Yn tonus to the ancestors of the Sym- 

 phyla, etc. Tlic Sympii.x la-Pauropoda group in turn has 

 departed but slightly from the ancestral condition of the 

 "Myriopoda" as a whole, although the ancestral ''My- 

 riopoda" comprised forms with bodies composed of 

 more numerous segments as well as those made up of 

 fewer segments. From ancestors similar to the mem- 

 bers of the Symphyla-Pauropoda group one line of de- 

 velopment has led to the chilopod type of myriopod, 

 while the other has led to the diplopod type. From their 

 ancestors related to the members of the Symphyla-Pau- 

 ropoda group, the Chilopoda have carried over man\ 

 characters also in*lierited by the ancestors of insects, so 

 that a structural study of tlio Chilopoda is of consider- 

 able value from tlic stniulpoiiit of iiisoct i)!iylogeny (as 

 is true to a l(->fi' (Ir-i'cc of tlto I )ii>lo! loda also). 



As was stated al)ove, the ancestors of tlie Insecta were 

 related to the members of both the Isopoda-Amphipoda 

 group (including the Tanaidacea) and the Symphyla- 

 Pauropoda group, so that the lines of descent of all three 

 grou])s (insects, iso]iods and Syni]»hyla) doubtless had 

 a connnon oriuin m Umn> intrrino.liab' l.ctwccn tlic Cu- 

 ]na<-ca and A nonio^t I'a.-a (and aU.. rclatrd to tlio Mysi- 

 dacea), and all of the tinve -i'oiip> liavo inlicritcd from 

 their common ancestry many diarartc.-- aUo rai-ried 

 over in the lines of develo])nH'nt ol' l!ic other two of the 

 three groups in question. The conimon ancotor- of the 

 three groups just mentioned (insocts. jsopods and Sym- 

 phyla) were not of any one sinulc typo, hut doubtless 

 differed quite markedly among thom-elvcs in the number 

 of segments composing their hodie-. tlic slender or 

 stouter and flatter character of the body an.d otlier fea- 

 tures. Some of them were more like the Tanaidacea. 

 while others were more like /Inl Jun/rlhi and otliei- mem- 

 bers of the Anomostraca. etc. and tlii- duud.! be <-learly 

 borne in mind in attemptiti- to determine uhat tl,<' an- 

 cestors of the in-ects. etc.. were lik.- for tile urealest 

 obstacle to arriving at the realization of the true nature 



