ABSENCE OF XENIA IN OSTRICH EGGS South African Ostrich Hens Mated with North African Ostrich Cocks Lay Eggs Characteristic of Their Own Species—No Signs of Male Influence on the Egg Shells—No Xenia J. E. DUERDEN, M.Sc, PH.D. Professor of Zoology, Rhodes University College, Grahamstown; Officer-in-charge, Ostrich Investigations, Grootfontein School of Agriculture, Middleburg, C.P.

N THE JOURNAL OF HEREDITY for North African ostrich from Nigeria May, 1915, Vol. vi, No. 5, appears with the object of possibly improving I a review of certain investigations on the domesticated Cape strains, built xenia in fowls. By xenia is there up during the past fifty years of ostrich understood "that the eggs laid by farming from the original South African a hen are influenced as to size, shape, wild bird. The imported birds, origi- and color by the cock with which she nally captured by the Arabs from wild is mated." The occurrence of xenia nests, were stationed at the GrOot- in plants is first noted. Here cross- fontein School of Agriculture, and the pollination is often found to have an breeding experiments in connection with influence on the character of the seed them were placed in charge of the writer! obtained directly from the cross, a Zoologists generally recognize four result which is shown to be readily ex- species of the ostrich genus, 'Struthio: plained'from the peculiar formation of The North African ostrich, 5. camelus, the endosperm, where one of the two Linn.; the South African ostrich, 5. nuclei from the foreign pollen is involved australis, Gurney; the East African in its production. The reviewer then ostrich, 5. massaicus, Naumann; and discusses the various instances which the Somali ostrich, S. molybdophanes, have been adduced as showing some Reichenow. The two last mentioned paternal influence on bird's eggs, espe- are however not well established species, cially those of Holdefleiss and Walther appearing to represent only intermediate with fowls and Armin von Tschermak types of the other two. On the other with canaries and finches. The conclu- hand the northern and the southern sion arrived at is that '' the evidence of birds have clearly defined distinguish- xenia in poultry is certainly not ade- ing characteristics as regards bodily quate." The article closes with the size and color, nature of the egg, and statement that "the question is a other minor features. Observing them recent one, and much work may yet be side by side as can be done at Groot- done on it, but until such work is done, fontein, without any intermediate forms, xenia in fowls must be considered an no one would hesitate in assigning them open question." specific distinction. Some recent work in crossing the As in all other birds the eggs from North African and South African ostrich the same ostrich and also from different upon which the present writer has been ostriches vary within certain limits as engaged for some time affords very regards size, shape and surface charac- conclusive evidence in support of the ters. But beyond these fluctuating above contention and, although dis- variations several well defined and tinctly negative in character, seems well constant differences distinguish the egg worthy of record, since it represents of the North African from that of the such a clear cut test case. In 1912 the South African ostrich; and it is the Government of the Union of South presence of these which affords such a- Africa imported 132 specimens of the decisive test as to the occurrence or 243 244 The Journal of Heredity otherwise of xenia. The egg of the group. The close grouping of the northern bird is always larger than that sunken pores gives rise to the deeply- of the southern, the shell is almost free pitted surface of the shell, often empha- from obvious pores or pittings, and sized in the nest by the adherence of presents an ivory-like, smooth surface. small particles of earth. Usually also the northern egg is rounder Whether the northern and the south- in shape or less oval, the two diameters ern ostrich are to be regarded as distinct being more nearly equal. On the other species depends largely upon one's hand the egg of the southern bird is conception of the term species. At any distinctly oval and is deeply pitted all rate the two are found to interbreed over the surface, the pits often larger freely and reciprocally, and the crosses and more plentiful around the air- or hybrids have also been proved to chamber end; and in consequence of the breed freely, both inter se and with pittings the surface does not present the either of the parent forms. About 200 ivory smoothness of the northern egg. eggs from the cross-matings have hither- Both however are of. the same cream to been obtained, both from Nigerian color when freshly laid, becoming lighter cocks mated with Cape hens and from on exposure. Among a number of eggs Cape cocks mated with Nigerian hens. from northern and southern birds mixed Breeding ostriches are kept apart from together no mistake could possibly be all others in large fenced camps, a made in separating the one kind from breeding set consisting of a single cock • the other. and one or two hens; and there is never As regards actual dimensions the any possibility of confusion as to the average long diameter of 43 northern pairings and the individual hen laying eggs was 6.15 inches and the short the twelve to eighteen eggs which con- diameter 5.35 inches; the average long stitute a nest. diameter of 22 southern eggs was 5.96 The nests are visited from time to inches and the short diameter 4.95 time to observe their progress, and in inches. Thus on the average the north- view of the possibility of xenia occurring ern egg is about one-fifth of an inch the characters of all the eggs have been longer and two-fifths of an inch broader closely noted. Without any hesitancy than the southern egg; the former has it can be stated that in no case have the an average weight of 3 pounds 11 ounces eggs shown any influence from the cock; and the latter of 3 pounds 3 ounces. northern hens mated with southern cocks The mean difference in the two dia- have always laid large, rounded, smooth, meters is 0.8 inch for the northern and unpitted eggs and southern hens mated with 1 inch for the southern, indicating that northern cocks have always laid smaller, the former are rounder or less oval than more oval, deeply pitted eggs. The the latter. experienced eye can at a glance dis- The pitting which gives such a tinguish one kind of egg from the other characteristic difference to the ap- as regards size, shape, nature of the sur- pearance of the two kinds of eggs is face and pitting; and in no instance have associated with the respiratory pores the eggs been different from those which of the shell. In the northern egg pores one would expect from the hen irrespec- occur, but are so small and open so tive of her mating, or even when un- close to the surface as to be scarcely mated. visible to the naked eye, and are mostly It can therefore be regarded as estab- scattered singly with but little grouping. lished that so far as concerns the egg of In consequence the surface appears the ostrich there is no evidence whatever almost uniformly smooth, though a fine of the phenomenon of xenia. The size pitting can be detected with a lens. In of the ovum, amount of albumen and the southern egg the respiratory pores nature of the shell are the characteristics are larger, sunken below the general of the hen just as much as are the surface and mostly in small groups, external bodily features, and are unin- varying from about six to twelve in a fluenced bv the cock with which she is Duerden: Absence of Xenia in Ostrich Eggs 245 mated. Knowing the facts of the case mating reveals itself, not in the egg laid this is certainly what any biologist by the parent hen with which the cross is would expect, though there is no a made. The average long diameter of priori reason why the presence of sper- 34 eggs laid by cross-bred hens is 5.99 matozoa in the oviduct should not inches and the average short diameter affect, the secretion of albumen "and shell 5.06 inches, which are practically the material; hence it may be that in other same as those of the southern egg (5.96; birds some undoubted influence from 4.95), but smaller than the northern the cock may yet be established and thus (6.15; 5.35); the average difference in constitute a true case of xenia. diameter is 6.93 inch as compared with EGGS FROM CROSS-BRED OSTRICHES the 1 inch of the southern and the 0.8 inch of the northern egg. Thus the size Naturally the fertilized germ within and shape of the cross-bred egg follow the egg from a cross-mating has very- those of the southern bird rather than different potentialities from the fertilized the northern. The pittings however are germ of a mating where both parents intermediate in number and depth. are pure, even though the shell is unin- Obvious pittings are found over the shell fluenced; and the ostrich derived from of eggs from cross-bred hens, compared the cross-fertilized egg has been found with their absence in the northern egg; to reveal the influence of both parents. The various dimensions and colors of but are neither so plentiful nor so deep the body and the characters of the plu- as in eggs from southern birds; the mage all show intermediate stages general surface is also more ivory-like between those of the northern and the than in the southern bird but not so southern birds, while a bald head-patch uniform as in the northern. occurring in the northern and absent The eggs therefore laid by a cross-bred from the southern is found to be domi- hen reveal undoubted influence from the nant, being present in all the cross-bred cross-mating; and the experiments have chicks. further shown that the characters are unaffected according as the cross-bred The egg laid by a cross-bred hen as hens are mated with cross-bred cocks regarded its size, form and surface is, as or with a pure northern or a pure south- observed above, quite as much a feature ern cock. The conclusion reached is of the bird as are the characters just mentioned, and may be expected to that in all cases the egg remains unaf- follow the one parent or the other of the fected by the cock bird, thus demonstrat- hen or partake of the nature of both. It ing the absence of xenia as unmistakably is here that the influence of the cross- as in the first cross-matings.