THE WINGS OF INSECTS 



383 



venation has been modified in other groups of insects than that which he is 

 studying; and that the easiest way to gain this knowledge is by a study of 

 a carefuhy selected series of wings illustrating these modifications. 



Having obtained the essential preliminary knowledge, the student can 

 then proceed profitably with his investigation. He should first determine 

 which are the most generalized wings to be found in the group of insects 

 that is being studied, the wings that most closely resemble the hypothetical 

 primitive type; and when this has been done, he should determine the 

 various ways in which the more specialized wings ha^x been modified. 



Fig. 406. — Fore wing of Pleronidea ribesii. 



In planning the work to be done in practicums accompanying a general 

 introductory^ lecture course, one is hampered by the limited amount of 

 time that can be devoted to each division of the more general subject. It 

 is obviously impracticable to require the students to make many drawings of 

 wings; on the other hand, it is essential that they should have practice in 

 determining the homologies of the wing-veins in a considerable number of 



/s/ ^ 

 Fig. 407. — Fore wing of Sirex. 



wings, if they are to gain a knowledge that will enable them to make use of 

 the analytical tables in the text books in which wing-venational characters 

 are used. 



We have met this difficulty by requiring these students to make draw- 

 ings of only one or two wings, just enough to give them a little experience 

 in the study of actual wings, and then furnishing them with figures of wings 

 in which the veins are not lettered. These figures are issued one at a time, 

 and each is to be properly lettered before another one is issued. 



Lettered figures of most of the wings used in this course are given in the 

 preceding pages; the others, two in number, are represented by Figures 406 

 and 407. 



