812 . DR. HANS GADOW ON OVARIES 



broad as is compatible with the upright walking and with the 

 flying organisation. Most likely the bi'oadness and the absence 

 of symphyses have been produced in adaptation to the eggs, but 

 even the distention of the belly downwards must be limited in 

 the bird, which is essentially and primarily a flying creature. 



Well, then, let us take it that it is advantageous that one of 

 the ducts and the activity of the corresponding ovary should be 

 suppressed. Instances of asymmetry, brought about by sup- 

 pression of one of originally paired organs, are common enough 

 in the Vertebrata, and they can in most cases be fairly explained 

 by mechanical factors. To refer them to mere accident, to a 

 toss up, which then becomes established, is too shallow a mode, 

 although not unprecedented in morphology. The tadpoles of 

 some Anura have paired " spiracles," others a median, the majority 

 a left hole. The reduction of one of the lungs of Snakes and 

 snake-shaped Lizards is of course directly correlated with the 

 shape of the body, and it appears almost optional whether the 

 right or the left lung should be affected, since both cases have 

 become established in the various groups. 



If we apply the principle of elimination of all those unfortunate 

 hen-birds which happened to produce eggs in either side, whilst 

 only those birds propagate the race which happen to have only 

 one side in working order, this would not explain the universal 

 right-sided suppression, which according to Gegenbaur is a 

 weighty argument for the monophyletic origin of the class*. If 

 we assumed this as a proof of their monophylism, we should 

 logically arrive not only at the imaginary pair of " Urvogel " but 

 also at the Eve of hens, which in her case would relegate the 

 establishment of the asymmetry to a toss up. During the 

 presumably long period of dawning bird-life such a one-sided 

 incipient suppression must have taken place over and over again 

 before it was firmly established. Inheritance, if not swamped 

 by panmixis, might have established asymmetry, but once more 

 we are groping in the dark for a cause which favours the left 

 side. It must be a factor which is very ancient and yet does 

 not interfere with the symmetry of the male organs, neither the 

 testes nor the vasa deferentia. Since the ovaries are strictly 

 homologous, or rather homogeneous, with the testes, this may be 

 taken as another hint that the ovaries are not the parts primarily 

 atiected. But the male ducts are not the same as the female ducts, 

 therefore the latter are indicated, No factor causing the 

 asymmetry can be derived from the vascular system, nor even 

 from the vestiges of the renal portal system, by the suppression 

 of which birds and mammals diflier from their common ancestors, 

 the reptiles. To refer the enlarged left ovary and duct to the 



* The suppression of one lung in Snakes, etc. stands on a ditferent footina:. It 

 may be due to an accident or sport, as much as right- and left-clawed crabs, or 

 rigiit- and left-twisted shells. The remaining lung enlarges and shifts its position 

 so as to occup3' most of the space originally intended for both. — H. G. 



