18 



THE TRACHEATION OF WINGS 



trachea tends to follow that of the medial trachea in its migration along the 

 transverse basal trachea towards the cubito-anal group (Fig. 7).* 



As the diagram representing the hypothetical type of the tracheation of 

 the wings wih serve also to represent the supposed primitive type of wing- 

 venation, there may be indicated in it the position of a few cross-veins, 

 which are so constant in their position, and which occur in so many widely 

 separated groups, that they are regarded as being comparatively primitive. 

 This is done in Figure. 10. 



None of the cross-veins are primitive in the sense in which the longi- 

 tudinal veins are primitive; for in the wings of the older Paleozoic insects 



Fig. 8. — Stenodictya lobata (After Handlirsch). 



there were no distinct cross- veins, but an irregular network of thickened 

 lines; this is weU-shown in the wings of Stenodictya (Fig. 8), which is 

 described in Chapter IV. 



In the older insect wings in which there are distinct cross-veins there 

 are many of them, and the few cross-veins that are referred to above, and 



*Enderlein ('02) has worked out with great care the tracheation of the wings of 

 Antheraea pernyi, a saturniid moth, and the connections of the tracheae of the wings 

 with the longitudinal tracheas of the body; and his account is illustrated by inost 

 excellent figures. 



In this highly specialized moth, media has completed its migration along the trans- 

 verse basal trachea and becpme a member of the cubito-anal group of tracheae. This 

 fact has probably misled Enderlein, for he argues at length that the veins of each wing 

 are separated "in zwei genetisch vollig verschiedene Systeme, das radiate und das 

 mediane Adersystem" (/. c. p. 28). He quotes the separation of the veins of the wing, 

 by Comstock and Needham, into the costo-radial group and the cubito-anal group, 

 but evidently overlooked our account of the migration of media; for he proposes the 

 division of the wing-tracheaj into a radial and a medial grotip, without any reference 

 to the facts that led us to make the division indicated above. 



