Vol. 1.] Woodwortli . — Wi7ig Veins of Insects. 77 



and Ephemerida, have a flexible area at the base behind, 

 which, if of considerable size, may contain one or more veins. 

 Very commonly there is more than one fold, in which case all 

 possess veins, except it be the basal one. The number of folds 

 may become very large when there is much disparity between 

 the size of the two pairs of wings, as in many Orthoptera. In 

 most beetles, in earwigs, and in some cockroaches the folds of 

 the hind wings lie in various directions in addition to those 

 radiating from the base, which we have just been considering. 

 The effect in all of these cases is the almost complete isolation 

 of each area bounded by folds. The fold thus produces a pro- 

 found effect upon venation. 



There are two distinct influences produced by folding. One 

 of these is the severance of the veins, already alluded to, and 

 the other is the production of new veins to define more sharply 

 the line of folding, as well as for the stiffening of the folded 

 area. These will be discussed in more detail when considering 

 the groups affected. 



One of the two methods of specialization recognized by 

 Comstock and Needham in the production of types of vena- 

 tion is the addition of veins. Adolph considers the maximum 

 number the primitive condition, so that all specialization 

 involves reduction. According to the theory of venation 

 offered in this paper, all venations may be considered to have 

 been produced by addition in the first instance, though in 

 most cases a subsequent reduction takes place. The theory 

 provides for indefinite increase or decrease along what may be 

 called normal lines; that is, by the duplication either of 

 posterior veins, of branches of existing veins, of independent 

 veins, or of cross veins, or by the suppression of these same 

 veins in the reverse order. This process can hardly be called 

 specialization, however, but rather simply normal increase or 

 decrease. Specialization is an unusual process producing 

 unusual results. A dragonfly possesses a specialized venation 

 with many veins, and a Psocid one with few veins; but it 

 can hardly be said that in the one case the securing of the 

 many veins, or in the other the loss of them, was the means 

 whereby their peculiarities were brought about. 



A true specialization by addition occurs in insects with 

 folded wings, where veins are produced in a manner quite dif- 

 ferent from the normal orderly manner in which new veins are 



