1909] Homologies of Wing Veins 127 



arisen are readily explained by this fact. Perhaps in no other 

 family could be found a clearer demonstration of the value of the 

 study of the tracheation in this connection. 



SUMMARY. 



The introductory discussion outlines the reasons for under- 

 taking this study of wing vein homologies, states the conditions 

 under which the study has taken place, and mentions some of the 

 difificulties involved in the manipulation of this sort of material. 



Attention is called to the coalescence of tracheae both the nor- 

 mal occurrence and some unusual instances. 



All the veins present in the four families discussed arc homo- 

 logized, each being taken up for detailed consideration and the 

 tracheal basis for the homologies being carefully stated. 



The historical discussion includes a notice of all such published 

 work as has any direct bearing upon this present paper. 



All the main features of venation or tracheation discussed are 

 illustrated by the accompanying figures. 



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