lEBEDAEY 8, 1907] 



SCIENCE 



221 



of specialization in a highly specialized 

 order. In the Paleozoic Protephemeridse the 

 author meets (and frankly acknowledges) con- 

 tradiction from the opposite end of the May- 

 fly series : " In one point, however, these early 

 wings stand in marked contrast with those of 

 the modern group. It is the absence of free 

 independents. The production of free inde- 

 pendents prior to connected ones would seem 

 to be the natural order of evolution, but this 

 evidence certainly does not point that way " 

 (p. 97). 



The author's account of their origin is all 

 comprised in the following sentence : " The 

 independents arise from the margin of the 

 wing, and might possibly be considered as 

 ingrowing branches of the marginal vein; 

 but, since this portion of the marginal vein 

 is commonly absent, while the independents 

 are almost always present, this conclusion 

 may seem to be unwarranted" (p. 68). 

 Nevertheless, his system is built upon it. 



But matters are still worse when viewed 

 from the mechanical standpoint. This theory 

 of veins ingrowing from the hind margin 

 contradicts the primary principle of insect 

 seronautics. For, as is well known, forward 

 motion through the air is due in insects 

 primarily to the sculling action of the wings 

 when vibrated up and down, and that action 

 results from the pliancy of the hind margin. 

 The trend of specialization in the wings of 

 all the orders is toward greater stiffness of the 

 front margin and greater relative pliancy of 

 the area behind it, and the obvious mechanical 

 advantage of this is that they scull in air 

 better. The disappearance of the marginal 

 vein and the fading out of the base of the 

 median, are, owing to position in the wing, 

 the earliest and most expedient contributions 

 to that pliancy. Girard more than half a 

 century ago demonstrated experimentally the 

 detriment to flight of adding weight to that 

 portion of the wing in which these ' inde- 

 pendents ' are supposed, according to this 

 hypothesis, to originate. 



The true order of development is inverted. 

 So it is in the case of the cross veins, whose 

 origin is discussed on page 71. These are 

 supposed, on this special creation theory, to 



grow up in the clear membrane de novo. 

 Special activities of certain cells, occupying 

 the positions that are to be those of veins and 

 cross-veins, are made to account for the ap- 

 pearance of these. But for the assumption 

 that the cells about the vein cavity show 

 greater secretory activity, or produce more 

 chitin, cell for cell, than those outspread in 

 the intervening membrane, there is no i^roof 

 offered: and it is not clear why the simpler 

 and long current explanation of the differ- 

 entiation veins from membrane, by accumula- 

 tion of cells about the vein cavities, and the 

 stretching of those that lie between, does not 

 give a better basis for the application of 

 mechanical principles. For how shall " the 

 more rational conception that there existed in 

 the beginning and has existed through all time 

 to the present day a mechanical necessity in 

 accordance with which the primitive vena- 

 tion was produced, and all its essential fea- 

 tures have been maintained through all the 

 vicissitudes of the ages " (p. 62) help us ac- 

 count for anything? It is merely a flow of 

 rhetoric : not an explanation. The mechanical 

 principle were better stated, or at least its 

 operations detailed, with some indications of 

 the material on which it operates. Through- 

 out this paper controlling mechanical prin- 

 ciples are heralded as though a new discovery 

 in insect wings, but they never come to light. 

 On the contrary, as we have seen, well-known 

 mechanical principles are flatly contradicted 

 by the theories proposed. Were it not that 

 the principle of vein differentiation is already 

 fairly well understood, this theory of ingrow- 

 ing independent veins might possibly have 

 made as large a contribution to the confusion 

 of the subject as did that of Adolph, its 

 lineal antecedent. 



A reviewer of vein mechanics should have 

 been able to see the primitive dichotomy of 

 the branching of veins. It is a curious survey 

 of insect venation that misses this. Dichot- 

 omy abounds in the venation of the oldest 

 known fossils. It occurs in the generalized 

 members of most of the groups. It occurs in 

 the gill covers of many Mayfly larvse and is 

 beautifully shown in those of Ephemerella. 

 It occurs in plants, also, and is the type of 



