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

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

As it is seen in the Table 1, the paired ovaries in the hybrid duck No. 59/62 are heavier and bigger than in duck No. 60/37. Whereas the surface of the smaller ovaries of the duck No. 60/37 was quite smooth, the surface of the bigger and heavier ovaries of the other duck, No. 59/62 has many bulges (swelling outs) (Plate 1). It looked like the ovary of a mammal. From the many bulges it could be concluded that the ovary of this animal functioned really as a normal ovary and had produced eggs (yolks) too, consisting, of course, only yolk substance. In the abdominal cavity there were four small yolk rests being in the state of a resorption and one normal yolk. It means that yolks after their detachment from the ovary were not able to reach the ostium of the oviduct. The oviduct of these genus-hybrid ducks was, inspite of its fully developed state, unable to function normally. Table 1. Body- and organ-weights of the two genus-hybrid females (Muskovy drake x domesticated duck) Organs No. 60/37 No. 59/62 Body-weight, kg 2. 37 3. 28 Skin with plumage, kg 0. 51 0. 77 Heart, g 17. 59 23. 67 Liver, g 38. 40 44. 57 Pankreas, g 7. 30 7. 95 Gizzard, g 63. 23 88. 15 Stomach, g 8. 23 6. 87 Intestine, g 33. 93 41. 85 Kidney, g 13. 35 18. 65 Brain, g 6. 82 6. 72 Hypophysis, mg 29. 3 63. 7 Thyroid, mg 258 251 Adrenals, mg 182. 0 355. 0 Ovary, right, g 0. 501 1. 530 Ovary, left, g 0. 832 1. 780 Oviduct (left only), g 1. 890 7. 200 As it is seen, in the organism of above-described genus-hybrid ducks a reversion occurred to the ancestral condition of Amniota's female reproductive type. The situation found in our genus-hybrid females reveals a deeper level of the phylogenetic sequence of this organ than the typical paired ovaries of some birds, which may be the result of the disturbed organisation of the ontogenetical processes caused by the disharmonie genotype consisting of two different genomes. Our findings described above confirm the hypothesis that organisms lacking different organs of their ancestors sometimes (if not in every case) possess factors in their genotype needed for normal development of these organs, but these factors are suppressed. CORMAN (1943) stated years ago that "conceivably all the genetic and developmental requirements for an atavistic character might be present, but suppressed in a specialised organism" (loc. cit. p. 90-91). It might be assumed that special factors which were present only in the offsprings of Muskovy drake No. 545/42, and which originated, without doubt, from this drake, were able to suppress - in the unbalanced intergeneric genotype - the normal avian factor determining the atrophy of the right ovary, but they did not prevent the total reduction of the right oviduct. Theoretically the situation may be more complicated. We have to suppose that in the course of avian evolution the ancient factor for paired ovarial "anlagen" had been suppressed by a newly formed genetical factor. And only later, in the course of the differentiation of special groups or individual genotypes under the influence of a given factor the suppressor genes became inactivated and the paired "anlagen" were able to escape the atrophy on the right side, too, and develop to a normal avian ovary (Fig. 1). The special genotype of Falconiformes may contain genetical factors which have a higher mutability for giving alleles of suppressor activity than that of the other groups of birds.