NO. 1687. THE THORAX OF rXS^FCTfi—^XODaRAS!!^. 549 



subject, and a study of the axillaries siui})ly coufiruis the results of 

 these authors derived froui a study of the venatiou it.self. 



The general relation of the veins to the axillaries is shown in text 

 figs. 1 and 5. The co.'ita {C) does not connect with any of them. Its 

 base very generall}^ forms a separate piece from the main costal shaft, 

 and is connected bj^ strong membrane with the preparaptera of the 

 pleurum. This separated costal head will be seen clearly by a review 

 of riates 04-09. 



The head of the subcosta {Sc) articulates with the anterior end of 

 the neck of the first axillary, except in rare cases of special modifica- 

 tion. (For typical examples see 184, 187, 201, 200.) The base of the 

 radius {R) is nearly alwaj^s more or less closely fused with the base of 

 the subcosta {Sc) , but it is clearly connected also in a great man}^ cases 

 with the anterior end of the second axillary (182-184, 185, 180, 192, 198, 

 203, 204, 208). In other examples its head is only contiguous to 

 the third axillary (185, 188, 191, 202, 209, 210, 211, 212). In a few 

 beetles the radius and second axillary are separated by a wude mem- 

 branous space (193, 194). 



The media (J/) and the cubitus (Cu) are closely associated w-ith 

 each other at their bases and wdth the median plates. A simple 

 arrangement is shown in the wings of Corydcdis cornuta (200, 201). 

 But both the media and the cubitus are so frequently fused with the 

 radius that their basal parts are difficult to determine in a definite 

 manner (180, 187, 202, 203, 205, 200, 207). In other cases they are 

 perfectly distinct at their bases (192, 194, 195, 198, 200). 



The first ancd vein (1-1) is separated from the rest of the anals in 

 the Orthoptera by the anal fold (see figures on Plates 47, 48). 

 The only apparent exception to this noted by the writer is in the 

 front wing of Gryllus (07). In the wing of a nymphal mantid (59) 

 the first anal (1-1) clearly arises at the base of the. wing, independent 

 from the rest of the anals. Comstock and Xeedham (1898, '99) 

 have shown the same thing in a drawing of the wing of a cockroach 

 nymph. The other anals generally arise from a common base, wliicli 

 is connected or fused with the third axillary. The vena dividens 

 (OO5 D) is not a primary anal, but a secondary vein developed in 

 the first anal fold (02, 04, 00, AF). In most other orders the anals 

 are fewer, and the first is not specially separated from the rest. 



The peculiar structure of the base of the wing in dragonflies will 

 be described under the Odonata in Section VII. 



VI. GENERAL CONCLUSIONS. 



1. The fourth head segment, apparent in some of the lowest insects, 

 is still regarded as a doubtful metamere by some embr^^ologists. 

 Assuming its genuineness, the following general statement seems 

 pretty well established : The head of insects is composed of six con- 



