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, sho \ving like phenomena), 

 and a single mounted wing of the common cranefly, Tipula, 

 with which to begin. 



FIG. 141. Venation of the wings of a series ot Psocids. /, Thyrsopsocu= , --, 

 Dictyopsocus; 3, Taeniostigma; 4, Epipsocus; j. Ptilopsocus; 6, Myopsocus. 7, 

 Psocus ; 8, Peripsocus; 9, Polypsocus; w. Calopsccus; //, Caecilius. 



