AND OVIKUCTS IN THE AMNIOTA. 811 



in ihm kommen Eier zur Reife, iind das rechte erhiilt sich nur bei 

 einzelnen (manchen Accipities,Schwimmvogeln uiid einzelnen Gat- 

 tungen verschiedener Abtheilungen) fort, indess es bei den iibrigea 

 verkiimmert. Dies steht in Zusammenhang mit der Ausbildinig 

 nur eines (des linken) Oviductes und mit dem bedeutenderen 

 Volum der Eier, wodurch jeweils nur einem einzigen ein liingerer 

 Aufenthalt in der engen Beckenhohle gestattet ist. Es ist also 

 hier die li'uckhilchiii.g einer I/al/te des gesamniten weihlicheii 

 GeschlechtsapjKtrates von der Ausbildung des Eivolums abhdngig, 

 und dadurch an einen hohei-en Zustand gekniipft, dass das nut 

 reichlichem Eiweiss und Dotter ansgestatte Ei das sich in ihm 

 entwickehTide Junge zu einer bedeutendeien Ausbildung gelangen 

 lasst." The correlations mentioned in these cumbrously involved 

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

 any further than where I had left it. 



Since the ovary is the prime organ and the duct merely 

 auxiliary, it might be assumed a prio7-i 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 ott' the 

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

 the soiii-ce. But, as we have seen, this does not agree with the 

 facts, considering the frequent activity of right ovaries, 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 reduction is an inheritance from reptilian ancestors, of 

 Avhich unfortunately we know nothing. Of recent reptiles only 

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

 These produce for one clutch a considerable 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 Chelonians, 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 proportion to its body 

 the eggs are enormous, especially in some of the nidifugoiis 

 groups which represent the lower conditions. They could not 

 well produce the whole clutch at once ; and they incubate 

 their eggs, not merely because they require seveial days, 

 even weeks, to produce 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 egg, leaving aside the inconvenience 

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

 overcome, a,s 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 



