O. Gy. Dely szerk.: Vertebrata Hungarica 23. (Budapest, 1989)

Stohl, G.: Some remarks of the paired ovaries of birds (Aves) 29-32. o.

VERTEBRATA HUNGARICA TOM. XXIII. 1989 p. 29-32 Some remarks on the paired ovaries of birds (Aves) By G. STOHL (Received 24 November, 1986) "Some remarks on the paired ovaries of birds (Aves)" - Stohl, G. - Vertebr. hung., 23: 29-32. 1989. Abstract: The role of special genetical factors in eliminating the effects of suppresors which normally cause the reduction of right ovary and oviduct in developing avian organism is discussed. A short description is given of two female intergeneric hybrids between Muskovy drake and domesticated duck having paired ovaries (=intersex organs? ) with a well-developed left oviduct. One of these hybrids had 5 yolks in the abdominal cavity four of which had been absorbed. It is well known that among vertebrates only birds have unpaired ovaries. From the paired "anlagen" of the ovaries being present in the first days of embryonic development the right one becomes rudimentary and after hatching young birds lose their right ovary with the corresponding oviduct. Consequently, in adult female birds all the eggs are produced in the left ovary and leave the abdominal cavity through the only functioning left oviduct. WITSCHI (1935) claims that the asymmetry characterising the sex glands of birds must be due to a primary, hereditarily fixed deficiency of the right cortical inductor. The deficiency of this inductor is then followed by an atrophy of the primordial germ cells of the right ovary. On the other side the asymmetry of the right oviduct might have evolved as an adaptation to the flying life habits of birds. An other author who also emphasises the adaptational character of the asymmetry of birds' female reproductive organs is WELTY (1964), who suggests that the reduction of ovaries is in part an adaptation to reduce ballast in a flying organism, but also an arrangement which protects the developing egg. Inspite of this ontogenetically well-regulated characteristic anatomical trait of the whole class Aves the occurrence of paired ovaries have also been found in female birds. From the wide-spread occurrence of paired ovaries in birds belonging to a number of families (according to KINSKY 1971: 12 orders, 86 species) at first, it may be concluded, that changes in embryological development resulting in paired ovaries are random events. Unknown alterations in the ontogeny result in paired ovaries, that is in suppressing the atrophy of the right ovary. Nevertheless, the fact that "without question paired ovaries have been found most commonly in the order Falconiformes" (KINSKY 1971, p. 336) seems to indicate the role of a special genotype in determining the development of paired ovaries. In the course of the evolution of certain birds the above-mentioned peculiarity of the genotype might have become a species character. Almost one and half century ago, in 1841, OWEN reported that a sectioned kiwi seen by him had two ovaries (cit. KINSKY 1971). All of these paired female reproductive organs are, viz. were typical bird ovaries, as it can be seen quite clearly in KINSKY's photos (1971) taken from the ovaries of sectioned kiwis (

Aptéryx sp., Apterygiforme

s). Kiwi species having paired ovaries produce of course normal eggs. If more than one egg is laid, ovulation occurs alternately in each ovary. How-