ANB OVIDUCTS IN THE AMNIOTA. 811 



in ihm kommen Eier znr Reife, und das rechte erhiilt sich nur bei 

 einzelnen (manchen Accipitres, Schwimmvogeln und einzelnen Gat- 

 tungen verschiedener Abtheilungen) fort, indess es bei den iibrigen 

 verkiimmert. Dies steht in Zusammenhang mit der Ansbildung 

 nur eines (des linken) Oviductes und mit dem bedeutenderen 

 Volum der Eier, wodurch jeweils nur einem einzigen ein langerer 

 Aufenthalt in der engen Beckenholile gestattet ist. Es ist also 

 hier die Hilckbildwiig einer Hidfte des gesanimten weihlichen 

 Geschleclitsapfarates von der Ausbildung des Eivolums abhdngig, 

 und dadurch an einen hoheren Zustand gekniipft, dass das mit 

 reichlichem Eiweiss und Dotter ausgestatte Ei das sich in ihm 

 entwickelnde Junge zu einer bedeutenderen Ausbiklung gelangen 

 lasst." The correlations mentioned in these cvimbrously involved 

 sentences are valid enough, but they do not cany the question 

 any further than vs^here I had left it. 



Since the ovary is the prime organ and the duct merely 

 auxiliary, it might be assumed a priori that the primary cause 

 of the reduction was the cessation of the production of ripe 

 eggs on one side, whereupon degeneration of the corresponding- 

 duct would follow, as there would be no longer any work for it. 

 Illicit, undesirable traffic is stopped best by cutting off the 

 supply, in the present case by the stoppage of ripening eggs at 

 the source. But, as we have seen, this does not agree with the 

 facts, considering the frequent activity of right ovai'ies, whilst 

 right ducts are much rarer. Further, we know that even com- 

 paratively far advanced ovarial eggs can be resorbed. Lastly, 

 we should have every right to expect birds with right, and others 

 with left functional organs. It cannot well be assumed that the 

 one-sided redviction is an inheritance from reptilian ancestors, of 

 which unfortunately we know nothing. Of I'ecent reptiles only 

 Crocodiles and Tortoises can be studied for the sake of analogy. 

 These produce for one clutch a considei'able number of hard- 

 shelled eggs which pass through both ducts. The eggs are well 

 protected, and there is ample room for them in the broad body 

 of Ohelonians, and there is likewise space and safety in the long- 

 belly of a Crocodile. 



Presumably therefore the cause of the asymmetry should lie in 

 the typical organisation of the bird. In projjortion to its body 

 the eggs are enormous, especially in some of the nidifugous 

 groups which represent the lower conditions. They could not 

 v/ell produce the whole ckitch at once ; and they incubate 

 their eggs, not merely because they require seveial days, 

 even weeks, to pi-oduce the full number, but because as warm- 

 blooded creatures they have reached a higher state of reproductive 

 organisation. There is no room within the pelvis for more than 

 one complete hard-shelled Qg^, leaving aside the inconvenience 

 of a right and a left egg which, for argument's sake, might be 

 overcome, as is actually the case with reptiles. The available 

 space in the bird's belly is limited ; the longitudinal distance is 

 relatively much shorter than in the majority of reptiles which 

 are devoid of a sacrum, and the peculiar pelvis of birds is as 



