Ill 



sideration have been developed. For additions to such a set 

 of veins may be made to the distal end of the series, or to 

 the proximal end, or may be interpolated at some distance 

 from either end. 



We will illustrate these principles by a figure of the wing 

 of a nymph of a cockroach (Fig. 10). We do not use for this 

 purpose a figure of a wing of a 'neuropterous insect, as that 

 would lessen the value, as a means of training, of the study 

 of neuropterous wings which the student is to make. A 



FIG. 10. Hind wing of a nymph of a cockroach. 



nymph is used here, because in the many-veined insects the 

 longitudinal veins, both primitive and accessory, are devel- 

 oped about tracheae ; and it is much easier to determine the 

 homologies of the tracheae of an immature wing than it is to 

 determine the homologies of the wing-veins of the adult. 

 And, too, in this way we are able to eliminate the cross- 

 veins which are not preceded by tracheae in the cockroaches. 

 Accessory veins added distally. If the radial trachea of tne 

 nymph of a cockroach be examined (Fig. 10, R\ it will be 

 seen that it bears many branches on its cephalic side ; each 

 of these branches is enclosed by a vein in the adult state. 

 The number of these veins is much gre'ater than that of the 



