— 82 — 



Fig. 5.— Wings of a May-fly. 



flies they are quadrangular (Fig. 5). This indicates that the longi- 

 tudinal, concave veins IV and VI were developed by a straightening 



out of the zigzag lines between two 

 series of cells in each case. In tbe 

 wings of modern May -flies, not only 

 have longitudinal, concave veins 

 been formed from zigzag lines, but 

 the cross-veins extending between 

 these concave veins and the adjacent 

 convex veins have become strictly 

 transverse ; this is an arrangement 

 which iusures the preservation of 

 the corrugations. 



Although it was shown that the 

 wing of a modern May-fly differs 

 essentially from the primitive type 

 of an insect's wing, and that the 

 veins premedia and postmedia are 

 absent in most of the orders of in- 

 sects it seemed desirable to base our nomenclature on the type con- 

 taining the maximum number of veins. The nomenclature of Red- 

 tenbacher was retained, therefore, with only such modifications as 

 were necessary. The most important of these modifications was the 

 omission of the numbers IV and VI in those cases where premedia 

 and postmedia are wanting. 



Spuler, however, failed to recognize the veins premedia and post- 

 media at all. In fact there is no evidence in his paper that he has 

 studied the wings of May-flies. He therefore numbers the veins as 

 they occur in the Lepidoptera without omitting numbers for premedia 

 and postmedia. 



In a recent paper* Dr. Packard has adopted the views of Spuler in 

 this respect. And I have come to feel that perhaps it would be 

 better for the sake of simplicity to refer to premedia and postmedia 

 by name only when speaking of the wings of May-flies, and to take 

 no account of them in numbering the wing-veins of other insects. 



A similar course has been taken already in the case of the humeral 

 zreins of the Lasiocampidae.f In this family of moths, longitudinal 

 veins have been developed secondarily in the greatly expanded humeral 

 angle of the hind wings (Fig. 6, h.v. ). These veins are referred to 

 merely by name, no account being taken of them in numbering the 

 principal veins. 



*A. S. Packard, On a Rational Nomenclature of the Veins of Insects, especially 

 those of Lepidoptera, Psyche, May, 1895. 

 ^Evolution and Taxonomy, p. 89. 



