ORGANIC EVOLUTION 



229 



Study 30. Determination of homologies of wing veins in 

 three series of closely allied insects. 



Materials needed: Enlarged prints of the wings figured 

 herewith (or of any other series, showing like phenomena), 

 and a single mounted wing of thecommoncranefly, Tipula, 

 with which to begin. 



4 



ii 



FIG. 141. Venation of the wings of a series of Psocids. 7, Thyrsopsocus ; s, 

 Dictyopsocus ; j, Taeniostigma; 4, Epipsocus; j, Ptilopsocus; 6, Myopsocus; 7, 

 Psocus ; 8, Peripsocus ; 9, Polypsocus ; JO, Calopsocus ; //, Caecilius. 



