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Shortness of the extremities in Dark Cornish fowls appears to be determined by several genetic factors, probably more than one of these being dominant over the long-legged condition. In short-legged Cornish tibia and tarsometatarsus are most strikingly shortened. The fibula is better developed than in ordinary chickens. One of the factors concerned in shortening of the long bones is lethal in homozygous condition. The lethal embryos die just before the end of the incubation period or are still living at hatching time but are unable to hatch. They show a striking shortening of the extremities. This lethal mutation is genetically independent of the Creeper mutation.

Eine vergleichende morphologische und histologische Untersuchung der Drusen mit innerer Sekretion normaler und chondrodystrophischer Huhnerembryonen am Ende der Embryonalentwicklung zeigte Anzeichen einer leichten Verzogerung in der histologischen Differenzierung von Thymus, Schilddruse, Epithelkorperchen, Hypophyse und Zirbeldruse. Der Hypophysenvorderlappen ist bedeutend kleiner als normal, und zeigt nicht unwesentliche Strukturveranderungen. Im ganzen scheinen die Befunde jedoch darauf hinzuweisen, das die Differenzierungshemmungen der innersekretorischen Drusen sekundarer Natur sind und nicht zur Erklarung der Entstehung der Misbildung herangezogen werden konnen.

Cyclopia and related malformations have been observed as a lethal condition of fowl. The more important facts and conclusions may be summarized as follows: 1. The morphological expression varied from a condition in which the upper beak was rudimentary to microcephaly. The whole gamut of defects is referred to as perocephaly. This is subdivided into two groups, viz. ‘rudimentary upper beak’, comprising the low-grade defects, and ‘cyclopia’, under which heading we include malformations ranging from synophthalmia to microcephaly. In the rudimentary upper-beak condition the premaxillary bones are lacking. On rare occasions such chicks hatched; they were always blind. Synophthalmia and cyclopia are associated with a proboscis above the median orbit. In more extreme conditions only a median pigment spot was present, there was no oral opening and the ears were closer to the ventral midline than normally (otocephaly). The most extreme cases were microcephalic without any indications of eyes, mouth or ears. 2. Perocephalic malformations made their first appearance inF 2 and later generations . of crosses between recessive rumpless fowl and representatives of the following three breeds: Silver Gray Dorking, Rhode Island Bed and Jungle fowl. In sibships which included any embryos with these malformations, the incidence was about 2–3%. When families with a different breeding history were intercrossed, the incidence of perocephaly rose to about 5 %, and upon combining the genotypes of all sources of origin the frequency became about 13%. The proportions of rudimentary upper beak and cyclopic embryos remained nearly constant during these changes in total incidence of perocephaly. After the 13% level of incidence had been reached, all but the smallest sibships contained perocephalic embryos. Significant heterogeneity of incidence continued, however, to exist between the individual sibships of pen matings. 3. Twenty-one sons of perocephaly-producing parents were tested in our experiments. All transmitted the malformations. 4. A rising incidence of perocephaly was associated with increased early embryo mortality. 5. The sex ratio appeared to be normal among perocephalic embryos of all grades. 6. A scrutiny of the data obtained during four years showed in three of them a highly significant seasonal trend, the incidence of perocephaly rising from early toward late spring. The causes of this trend remain uncertain. 7. The results of our breeding tests led to the following interpretation. The genetic factors responsible for the occurrence of perocephaly (possibly a single recessive gene substitution) were present in the stock of recessive rumpless fowl. Except for extremely rare ‘ sporadic’ occurrences, the mutation was completely suppressed by modifying genes. The mutation came to light after outcrosses to unrelated stocks and the incidence rose with continued dilution of protective modifiers. It is evident that even in later generations many embryos which were homozygous for perocephaly developed normally. 8. It is suggested that, in fowl at least, the accumulation of recessive modifying genes with individually small effects, but which in concert can completely suppress the action of deleterious mutants, represents a common and important mechanism of equilibration and genetic self-defence.

Eine vergleichende morphologische und histologische Untersuchung der Drusen mit innerer Sekretion normaler und chondrodystrophischer Huhnerembryonen am Ende der Embryonalentwicklung zeigte Anzeichen einer leichten Verzogerung in der histologischen Differenzierung von Thymus, Schilddruse, Epithelkorperchen, Hypophyse und Zirbeldruse. Der Hypophysenvorderlappen ist bedeutend kleiner als normal, und zeigt nicht unwesentliche Strukturveranderungen. Im ganzen scheinen die Befunde jedoch darauf hinzuweisen, das die Differenzierungshemmungen der innersekretorischen Drusen sekundarer Natur sind und nicht zur Erklarung der Entstehung der Misbildung herangezogen werden konnen.

Linkage tests were made between the genes for single-comb and for the Creeper condition in fowl. Four geographically different lines or Creeper chickens were used in the matings. Chickens which were heterozygous for Creeper and rose-comb were crossed to others which were homozygous for the two recessive genes (normal skeleton and single-comb). Both heterozygous males and females were used in these back-crosses. The experiments extended over the first and second laying year. The total progeny of these matings amounted to 6627 individuals.

Bei homozygoten Embryonen des Kruperhuhns wurden neben Misbildungen der Extremitaten (Phokomelie) und des Schadels solche der Augen gefunden. Bei diesen Augenmisbildungen handelt es sich um Fehlen der Lider, Mikrophthalmus, Coloboma fundi, Fehlen des Skleralknorpels usw.

The duplicate mutation (Po d) of fowl is responsible for preaxial polydactylism of hand and foot Malformations of the radius occur frequently in association with finger duplication, These abnormalities can be arranged in series which in one direction lead by imperceptible steps from a slight hypoplasia to aplasia of the radius and which in the opposite direction proceed from the occurrence of small supernumerary rudiments to complete radius duplication. The duplicated radius may have a grossly abnormal, broad and flat shape with irregular outline.

THE fact that cortisone has an inhibitory effect on growth of chicken embryos was first noted in 19471. A detailed study of this phenomenon was afterwards undertaken by Karnofsky, Ridgway and Patterson2 and their observations were confirmed by Yamada3 and by Siegel, Smith and Gerstl4. Cavallero, di Marco, Fuoco and Sala5 secured evidence indicating that the growth-inhibiting effect of cortisone is brought about by an interference with protein synthesis, and an excess of hydroxyproline found by Roberts, Karnofsky and Frankel6 after cortisone treatment presumably points to the same conclusion. In experiments with weanling rats, Tuchmann-Duplessis and Mercier-Parot7 failed to counteract the growth-inhibitory action of cortisone by concurrent treatment with somatotropic pituitary hormone, glucosamine or the polysaccharide fraction of human placenta. In chicken embryos, on the other hand, Sobel8 observed that the deleterious effects of cortisone on growth and survival were partially counteracted by simultaneous administration of somatotropic pituitary hormone.

TREATMENT with insulin has well-established teratogenic effects in chick development. When administered during the earliest stages of incubation (first 2 days), it is responsible for the occurrence of rumplessness (chiefly absence of the tail vertebrae), whereas somewhat later (4th or 5th) day) it leads to a syndrome of micromelia and abnormalities of the beak (namely, a shortened upper beak or parrot beak). During these later stages, but not in the early ones, the teratogenic activity of insulin is strikingly exaggerated by the simultaneous administration of chlorpromazine1. The amounts of chlorpromazine which produce this effect were non-teratogenic and only moderately toxic if given alone.

Recently we have reported on linkage tests between the genes for single comb and for the creeper traits in fowl1. Afterwards, the back-cross matings of heterozygous rose-combed Creeper hens to Leghorn cocks were continued through the third laying year of the hens. During this period we obtained a total of 781 offspring (hatched chicks and classifiable dead embryos), distributed as follows: There was 0.38 per cent of crossing-over. These data added to our earlier ones bring the total off-spring of matings between heterozygous Creeper females and normal males to 4,313 individuals with 0.56 per cent of crossing-over, and the total offspring of all back-crosses to 7,408 chicks with 0.39 per cent crossing-over.