576 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxix. 



The cells of the wing are named by applying to them the abbrevia- 

 tions of the vein forming its front margin, the group of cells at the 

 base of the wing (fig. 1), being designated by the abbreviations of the 

 principal veins, while the group of cells at the apex of the wing are 

 designated by the branches of the veins. It should be borne in mind 

 that when the vein forming the front margin of a cell is a composite 

 one, as R2+3, the cell behind this vein is not R^+s^ ^'^^t R3, the cell Rg 

 having been obliterated b}^ the coalescence of the veins Rg and R3. 

 When cells are divided by a cross-vein, as cell M^, the basal portion is 

 spoken of as 1st M^ and the marginal portion as 2d M,. In labeling 

 the figures of entire wings, the names of the veins are put either on 

 the veins or near them, and an arrow placed to indicate the vein to 

 which the name applies, or at their apices around the wing margin, 

 while the names of the cells are placed within the cells to which they 

 apply. 



All that portion of a vein that does not coalesce with any other vein 

 is spoken of as the free part of that vein. If media be taken as an 

 example, then all that portion of Mj between the point where it sepa- 

 rates from Mjj and the margin of the wing would be the free part of 

 Mj. In the following pages the origin of particular veins is frequently 

 spoken of. B}' this is meant the point or place where they separate or 

 fork and does not refer to the actual point of origin. If media be 

 taken again as an example, the point where Mj separates from Mg 

 would be considered as the origin of the free part of Mj. 



Although there are no facts in support of the method here given, 

 and although it implies a condition much more generalized than is 

 found in the hypothetical type, yet I have always found it easier in 

 working out the homology of veins m3'self, and also in explaining 

 venational problems to others, to consider each of the branches of any 

 vein as extending from the base to the margin of the wing. If radius 

 and its five branches be taken as an example, the stem part, always 

 designated as R, would ])e considered as being a combination of all 

 the branches of radius, or as Rj+g+^+^+j. which divides into Rj and Rg. 

 In like manner the stem of the radial sector would be considered as 

 being a combination of all the branches of the radial sector, or as 

 Ro+3+4+5, which divides into R3+3 and R^+r,, and these in turn into R^ 

 and R,, and R^ and R., respectively. So that in tracing out the course 

 of any of the branches of radius by drawing a pencil along them, as R^, 

 beginning at the base of the wing, we would pass first over the stem 

 of R, then over the stem of the radial sector, then over R4+5, and 

 finally over the free part of R^. 



