174 



THE AMEBIC AN NATURALIST 



[Vol. LIIl 



nearer to the ancestors of the ''acridids," although the 

 line of development of the latter may have branched off 

 from a ''locustid" stock. The Phylliwn-li'ke forms seem 

 to be modified phasmids which have certain features in 

 common with the grasshopper group. 



The plecopteroid, blattoid and orthopteroid groups are 

 all very primitive, and are so intimately connected by 

 intermediate forms or synthetic types that they are to 

 be considered as representing one section of the Ptery- 

 gota, to which the term '^Plecopteradelphia" was ap- 

 plied (Crampton, 1916a) to indicate that they are the im- 

 mediate descendants of Plecoptera-like ancestors and the 

 ephemerids and Odonata should doubtless be included in 

 the same section of the Pterygota, There is a bare pos- 



sibility that the blattoid forms rather than the Plecop- 

 tera are nearer the ancestral type from which the others 

 were derived, but the close resemblance of immature Ple- 

 coptera to lepismids, and the very primitive organization 

 of the Plecoptera, make it very probable that they, rather 

 than the blattids, represent very closely the ancestral 

 forms which ga\'e rise to the blattids themselves, and the 

 other ty])es meiitionod above. The higher insects were 

 a]<o ni)parently descended from forms ultimately de- 

 rived from ancotor^, related to the Plecoptera, but they 

 have "clustered togethei'" in another division forming 

 tlie "Xeur()i)terade]pliia" (('rami)ton, .U)1Ga) or forms 

 grouped about the Xeuroptera in the second section of 

 winged insects next to be considered. 



The members of the second section (or ''Neuroptera- 

 delphia") fall into two principal groups. One of these, 

 comprising the psocids. Tliysanoi)tera, and hemii^teroid 

 forms, were probably descended from ancestors not un- 

 like the psocids. and it i- iil^o niiiK- i.o^^il.K. tliat the Mal- 

 lophaga, and liic Aiioplcui-a or '"Sipliniiciilata,'' rep- 

 resent offslKjot- of till- -lock. Tlii> grouj) had a common 

 origin with the neuroi^teroid insects (probably from 

 Pleco])tera-like forebears) and the two paths of develop- 

 ment have extended side l)y side for a considerable dis- 

 tance, both having numerous characters in common. 



