230 GENERAL BIOLOGY 



First, draw the wing of Tipula, carefully, to see the nature 

 of the material under consideration; for the others, to 

 save time, use the figures, which are reasonably accurate. 



Then begin with the cranefly wings series. Carefully 

 label the veins in each wing with the proper abbreviation at 

 base and apex; do this lightly in pencil, subject to 

 later correction. Mark fusions of branches with the plus 

 sign between the numerals of the branches conjoined. 

 Determine homologies carefully. Follow each main vein 

 stem outward and see when and how often it forks. The 

 proof of correctness will consist in having all parts of the 

 typical wing present or accounted for. Omit to name a 

 vein or branch only when it is considered to have disappeared 

 by atrophy; in this series and the next following, veins M4 

 and 3d A may be so treated. Note particularly that the 

 cross veins are all in their proper places, or accounted for. 

 When correctly interpreted the series will be consistent 

 and harmonious, and the correctness of it will be obvious. 



Finish the work by coloring the veins alternately in two 

 different colors, and making the cross veins a third color. 



Repeat, with the second series of miscellaneous fly wings. 



Repeat with the third series, of psocid wings, (fig. 141) 

 noting here in the beginning that median and cubital veins 

 are fused together in all members of the series from near the 

 base outward well across the wing. 



The record of this study will consist in the one drawing 

 and in the coloring and lettering of the veins on the prints, 

 and these are to be preserved as material to be used in a 

 subsequent study. 



The serial homology of the higher crustaceans. 



Serial homology is characteristic of the group of the higher 

 Crustacea known as the sub-class Malacostraca, and this 

 group well illustrates how a single plan of structure may run 



