OVARIES IN CERTAIN DRITISU BIRDS. 67 



excretion of urea can be carried on by one kidney if the other be 

 destroyed by disease, or removed in its entirety by the siiroeon ; 

 but the animal with one kidney only is admittedly less well oil' 

 than the animal with the normal pair. The life would be called 

 a bad one at any vertebrate life insurance office, and the premium 

 charged would be correspondingly high. Two ovaries may not be 

 a necessity, but they must be better than one. The suppression 

 of the second ovary appears to be a retrograde step for which it is 

 hard to find any adequate reason, and is almost without a parallel 

 in vertebrate embryology. 



In dissecting an immature female Sparrow-hawk {Accipite?^ 7iisif,a) 

 (plumage of the first year) shot on the 9th of January, 1892, J 

 found both ovaries equally developed, containing small eggs of 

 uniform size. 



In the following April a second example came under the notioe 

 of Mr. F. Menteith Ogilvie, who had happened to be with me 

 when I skinned and examined the former specimen. He made 

 the following note :— "April 11th, 1892. I dissected A. oiisiis $ . 

 Both ovaries well developed, eggs numerous and of various sizes— 

 I think the forward condition of the ova shows the bird would 

 have bred this season, though it was certainly only a last year's 

 bird." 



From 1892 up to the present date I have paid special attention 

 to the sexual organs of all birds passing through my hands, in 

 order to investigate the condition of the female generative sj^stem, 

 the frequency with which the right ovary was found to persist^ 

 and the species in which such persistence occurred. In every case 

 where paired ovaries were found I took notes and made as accurate 

 sketches as I could with the specimen on the table before me. 

 In 1895 and again in 1903 I recorded a number of these 

 instances in two papers read at meetings of the Norwich Science 

 Gossip Club*. Since then further examples have been added, 

 bringing the total number of specimens with paired ovaries in my 

 series to. 45. These are grouped in bulk in Table I. (see p. 72), 

 and are separately treated in detail in the Appendix. 



Neither Table I. nor the Appendix includes several instances in 

 which I have found the two ovai-ies in certain nestlings. 



On July 7th, 1909, six nestling Sparrow-hawks with their 

 parents (second year's plumage) were sent me from Suffolk 

 (see Appendix lO"). In sexing the nestlings I found that five 

 were females and the sixth, a much smaller bird, a male. All 

 the five female nestlings had paired ovaries, the glands averngino- 

 half an inch in length. They were equally developed and easy to 

 recognise. The excessive proportion of females over males in the 

 Sparrow-hawk in this instance is noteworthy — I have observed 

 the same fact on a former occasion t, in which, out of sU nestliug.s 

 four were females and two were males. 



* Report of Proceedings, May 1895 ; M.iy 1903. 

 t 'Zoologist,' 1885, p. 51. 



