1907.] ox THE ORIGIX OF FLIGHT. 22ii 



(8) As a general rule tlie entrance of the azygos vein or veins 

 into the precaval or pi-ecavals is more anterior in position in 

 Mammals, occupying a lower position in the series than in more 

 specialised types, i. e. opposite to second rib instead of fifth or 

 sixth. This corresponds with ontogenetic shifting back of heart 

 and blood-vessels. 



(9) The conditions observable in the newly-born young of 

 Myopotainus coypu seem to show that the postcardinals may - 

 persist as such at least up to the time of birth, and in some adult ~Tj 

 Rodents one is also persistent. ^ 



(10) The same species shows that the azygos of the adult is -4 

 independent — except for a very short tract at its opening into the 



precava — of the postcardinal of its side, thus confirming the embryo- ^^ 



logical results of othei'S who have affirmed that only the very ^^ 



commencement of the azygos is traceable to the persistent post- '"^ 



cardinal of its side. -^ 



(11) It is probable that the veins called "azygos" in adult o 

 Mammals are not in every case strictly homologous veins. Whei-e C/? 

 there is but one azygos present (e. g. Carnivora) it is probable (;^ 

 that that vein is the true azygos, except in the abdominal region § ^ 

 where it is formed by the persistent postcardinal. In cases whei-e '"k^ C\) 

 there are two azygos \eins both may be (? certain Marsupials) -^ L^ 

 persistent postcardinals, oi- one of the two may be a remnant of 9 cs 

 the postcardinal, the other being a true azygos. ]\J ^ 



(12) These and some other facts and conclusions lead to the 11 

 inference that the true azygos vein of Mammals {%. e. that formed ;t^ £> 

 by an outgrowth of the postcardinal) is a structure which has been ^ 

 developed in the Eutheria. ^ 



5. Ideas on the Orioin o£ Fliorht. 

 By Dr. Baron Francis Nopcsa. 



§0 



[Received February 8, 1907.1 U 



(Text-figures 74-82.) rx 



Although much has been written on the origin of flight, 

 yet till now no really satisfactoiy explanation foi- this kind of 

 locomotion has been found. This is, so far as I can under- 

 stand, mainly due to the fact that it has on a j^riori grounds 

 been svipposed that all the principal groups of flying vertebrates — 

 namely, Pterosaurs, Bats, and Birds — originated in a similar 

 manner, without fully appreciating the fundamental fact that, 

 from the viechanical standj^oint, patagiam and feather are two 

 perfectly different organs. 



A patagium is a soft flexible membrane and in consequence 

 requires, to be effective, numerous firm radial supports originating 

 from the body that has to be carried, whereas for a series of 

 semirigid but elastic quills one line of attachment is sufficient. 



In consequence of this difference, a patagivim-flyer must always 



