I'EBBUARY 8, 1907] 



SCIENCE 



219 



origin of wings, their relation to the body, 

 the mechanics of flight, the basal articulation, 

 vein structure, vein development, the genesis 

 of venation, methods of modification, and 

 venation types. It presents some new and 

 interesting data on the nature of degenerate 

 and metamorphosed veins, and more especially 

 on the mode of articulation of the wings with 

 the thorax; but, in the main, it is a purely 

 theoretical discussion of certain classes of 

 facts previously well known. Professing to 

 be based on studies of twenty-two years, on 

 " microscopical preparations of about two 

 thousand species representing all the principal 

 groups, a much larger series of insects with 

 spread wings, and practically all the pub- 

 lished figures of insect wings," it is singularly 

 parsimonious of new facts. 



The theory is, in brief, that insect wings 

 have arisen from tracheal gills, that the veins 

 are inherited from gill covers and have no 

 connection with the trachete inside, but that 

 " mechanical necessities are the dominant fac- 

 tor in their first production and in their sub- 

 sequent development," and that the venation 

 collectively evidences three major groups of 

 winged insects, called by the author Neurop- 

 tera, Elytroptera and Neoptera. 



Gegenhauer's theory of the origin of wings 

 from tracheal gills is accepted, and is defended 

 probably about as well as is possible in absence 

 of good evidence. The gill cover of a single 

 species of Mayfly larva of the genus Bithro- 

 gena is used in illustration. Unfortunately, 

 this gill cover is one of the most highly spe- 

 cialized for its own peculiar functions, and is 

 quite off the line of possible wing develop- 

 ment. Its basal articulation is said to be like 

 that of wings, but it is not described. The 

 diagonal brace across its lower face, cited as 

 ' most cojivincing evidence ' of its relation 

 with wings, would be much less convincing 

 with a little more knowledge of gill covers. 

 Still, notwithstanding that the choosing be- 

 tween theories in this' field is a matter of bal- 

 ancing remote possibilities, the presence of 

 basal articulation and musculature in gill 

 apparatus gives the Gegenbauer theory an 

 advantage over Miiller's lateral expansion 

 parachute theory. But it does not appear 



why the suggestions of Dr. Tower, published 

 some years ago in this same series of con- 

 tributions, should not have been noticed. 



The author's treatment of the wing tracheaa 

 is somewhat remarkable. He reluctantly ad- 

 mits that these air tubes sometimes grow in 

 wings, but he does not allow them to appear 

 in any of his wing figures — only in the Mayfly 

 gill cover; and there, apparently, because not 

 coincident in position with the brace which he 

 thinks is like a primitive vein. He seeks by 

 argument as labored as it is unnecessary to 

 prove that they have no air-taking function, 

 while quite ignoring their air-distributing 

 function. Everybody knows that in insects 

 air is carried to all the living tissues of the 

 body, not in blood vessels as in vertebrates, 

 but in tracheae, and the equanimity with 

 which, throughout this whole discussion, these 

 principal visceral organs of the wings are 

 excluded from consideration is most remark- 

 able. A few quotations will illustrate this: 

 " In many wings, at least, tracheation is a 

 comparatively late and entirely secondary 

 matter" (p. 7). Quite true; but in what 

 wings? In none but those of a few highly 

 specialized groups. Teeth are absent from 

 the jaws of some mammals; but their absence 

 is not better accounted for, nor more dis- 

 turbing. 



" In studying the development of veins, we 

 need only to take into consideration the con- 

 stant features of the developing wing, the 

 hypodermis of the wing pad and the cuticle 

 that it secretes" (p. 52). 



"Accidents of structure of a temporary 

 adaptive organ" (p. 62). The italics are 

 mine. 



" The venation is conceived of as receiving 

 nothing" from the precursor of the wing except 

 veins that were developed in the same way 

 and to meet the same needs with those of the 

 organ after it became adapted to flight" (pp. 

 144). 



He laments that in adopting the Miillerian 

 hypothesis Packard was " not entirely able to 

 divest himself of his former idea of an essen- 

 tial connection between trachese and veins " 

 (p. 62). Alas, Packard was not able; neither 

 was that ' prince of entomologists,' Dr. Hagen ; 



