NO. 2 THORACIC MECHANISM OF A GRASSHOPPER — SNODGRASS 89 



sists of a single branch (M) given off from the radial sector {Rg)- 

 Between the basal radio-medial shaft (R + M) and the first anal 

 fold, there are two veins in the cubital area (iCii, 2C11) ; the first 

 (fig. 47 B, iCii) is united proximally with the radio-media, the second 

 (<?Cw) has no basal connections. In the hind wing, therefore, as in 

 the forewing, there are two distinct cubitals, here named the iirst 

 cubitus (iCu) and the second cubitus {2C11). Each of these veins 

 is represented by a trachea in the hind wing of the nymph (fig. 46 B) ; 

 the first is the "cubitus" {Cu) of Comstock, and the second the 

 " first anal " {lA). Since both of these veins lie anterior to the anal 

 fold in the adult wing (figs. 45 B, 47 B), however, the writer would 

 agree with Tillyard (1919) that the second is a cubital rather than 

 an anal vein. The orthopteran wing suggests that the second cubitus 

 has the status of an independent vein rather than that of a basal 

 branch of the first cubitus. 



The anal fold of the hind wing is double (fig. 50 B), consisting of 

 two plicae, or lines of flection in the wing membrane, between which 

 lies the vena dividens (figs. 45 B, 47 B, 50 B, VD) . According to Till- 

 yard the vena dividens is the " first anal," but since it has no basal con- 

 nection with the other anals (fig. 47 B), the writer would regard it 

 as a secondary, interpolated vein. The incomplete vein of the fore- 

 wing lying just behind the anal fold (fig. 47 A, s) may represent the 

 vena dividens of the hind wing, but it appears rather to correspond 

 with the vein i of the hind wing (figs. 45 B, 47 B). 



The anal veins of the hind wing form a distinct group lying pos- 

 terior to the anal fold. All the primary anals spring from a basal sup- 

 port (fig. 47B, q) which is attached anteriorly to the distal arm of 

 the third axillary (jAx), and which, in the grasshopper, is braced 

 posteriorly by an arm from the tergum (figs. 24, 47 B, p). There 

 are ten primary anal veins. A fork from the first (lA) divides into 

 three branches (i, j, k) lying in the first lap of the wing that folds 

 beneath the preanal region when the wing is flexed (fig. 50 B). Al- 

 ternating with the primary, or " convex," anal veins are nine secon- 

 dary " concave " veins lying in the troughs of the folds between the 

 primary anals, while the vein (k) branching from the first anal is the 

 concave vein of the fold between the vena dividens and the first anal 

 (fig. 50 B,^). 



Articulation of the wings. — In the membrane of each wing base 

 are four axillary sclerites. The first and the fourth (fig. 47 A, B, lAx, 

 4Ax) are hinge plates articulating with the edge of the tergum ; the 

 second {2 Ax) is the pivotal sclerite of the wing base ; the third {sAx) 



