OVARIES IX CERTAIN BRITISH BIRDS. 09 



a signalman refuses to accept a new train until his section is 

 cleared of the ohl one. 



(c) Finally thei'e remains the question whether one oviduct can 

 serve two ovaries. There is not much evidence for or ngainst this 

 supposition. 



In some cases the appearance of the paired ovaries rather 

 suggests that both had taken part in discharging ripe ova, while 

 only one oviduct shows much development. 



On the other hand, the normal involution of the oviduct is so 

 exti-aordinarily rapid, that in some specimens with well-developed 

 ovaries, which are known to have passed the last eggs of their 

 clutch quite recently (S*"), the oviducts on both sides are merely 

 represented by ill-defined sti-ands quite difficult to differentiate 

 macroscopicaliy from the surrounding tissues, and but little more 

 marked than the oviduct (or ducts) would be in the autumn and 

 winter months. 



The upper portion of the oviduct is provided with a mesentery 

 ■which is sufficiently long to allow a very considerable amount of 

 free play. There seems no physical objection to the open end of 

 the tube {ostium abdoninale) swinging across the mid-line of the 

 spine *, and grasping the ripe ovum of the opposite ovary with 

 nearly the same facility as the ovum of its own side. 



Extra-tubal gestation, by which I mean the shedding of a ripe 

 ovum into the peritoneal cavity, is, so far as we know, an 

 exceedingly rare accident among birds. Dr. Wilson t mentions 

 such a case. 



Two functional ovaries and one duct collecting eggs from both 

 sides would be exactly the conditions which would predispose to 

 such an occurrence. 



Returning to the paired ovaries, it is manifest that these cases 

 are not exceedingly rare among many quite widely separated 

 groups of British birds. In one family, the Falconidse, such 

 instances may be termed positively common. One cannot help 

 realising that if 45 examples come under the notice of one man 

 in the course of nineteen years, double ovaries must be something 

 more than of occasional occurrence. 



The obvious conclusion seems to be that they are not found 

 because they are not looked for. 



In the writings of English ornithologists I can find but one 

 specific record (and that a very recent one) of paired ovaries. 



Dr. C. B. Ticehurst J describes three cases in which he found 

 the right ovary persisting — all three examples were Sparrow- 

 hawks. 



* Except in the Falcnnidfc the examples of paired ovaries generally show an 

 asymmetrical state of affairs, with the right ovary belnw the left, and at the same 

 time carried over somewhat laterally from right to left. In such cases as these tiie 

 left oviduct woul.l have no further to go for the eggs from the right ovary than lor 

 those from the left. 



+ •Grouse in Health and Disease,' p. 183. 



-^ ' British Birds,' November 1910. p. 18?. 



