THE CANADIAN ENTOMOLOGIST. 291 



not go either way, but obstinately retains its original primitive central 

 position. This happens in the Skippers and Noctuids. The result is 

 that the vein becomes isolated by the disintegration of the supporting 

 discal cross-vein, a process which is never stayed. Then the second 

 median branch, deprived of support and nutriment, fades away. For 

 particulars of this theory of the movement of the median branches, see 

 various articles issued by me in the years 1897 to 1899. The radial 

 position is assumed by the Pierids and Nymphalids, a.Iso the Nemeobiidae. 

 The cubital, by the Papilionides and Dismorphians, which latter include 

 Leticophasia. The central position is retained by the Skippers, apparently 

 yielding to the cubital in the Megathymidse. The movements of the 

 radial branches and the median may be traced in all lepidoptera. 

 Although I have worked them out chiefly from the diurnals, they are 

 intelligible only as part of a system generally applicable All genera of 

 butterflies show the wings in comparative stages of advance in this 

 respect. For instance, let us compare the wings of Parnassius with 

 \.\\o%Q. oi Papilio. These movements, which are frozen in the Swallow- 

 tails, are released in the Apollo butterfly and its kindred ; in other 

 words : Parfiassius is seen to be here the specialized and Papilio the 

 relatively generalized form I say relatively, because all these changes 

 are gradual and one form must be compared with another to ascertain 

 the difference in extent of these two movements. The grades are 

 innumerable, established by the delicate differences of these natural 

 instruments of measure. Another truth, which I have dwelt upon else- 

 where, may now find its place : The specializations, of the two systems 

 and of all other features in the wing, are ujiequal. This prevents snap 

 judgment as to which is ahead, and which is behind, when we discuss the 

 position of different groups and endeavor to establish it by a single 

 feature. Rank is not an absolute and determinable condition in all 

 cases ; the specializations of moths may exceed those of butterflies. 

 Moths may represent younger forms and butterflies may be older than 

 we might suppose. We now come to 



The anal veins, 

 which are theoretically four in number. The first anal (submedian fold) 

 has disappeared as a vein, and appears only as a fold in most generalized 

 forms. The fourth and third anal veins depart one after the other ; the 

 second anal is alone permanent. The Hesperiades have two anal veins 

 remaining, the second and third ; the Papilionides only one, the second. 



