156 Vererbung, Variation, Mutation. 



The experiments began by crossing Himalayan rabbits (white with dark 

 points, pink eyes), with yellow and "tortoise". Tortoise is a yellowish rabbit 

 with dihite black pigment especially on the points. The experiments indicate 

 that three factors are concerned: A, the "agouti" factor which turns Ijlack into 

 agouti, and tortoise into yellow; E, a factor for extension of melanic pigment, 

 which turns yellow into agouti, and tortoise into black; D, a factor which inten- 

 sifies the melanic pigment. The most novel results concern the factor D, which 

 was introduced by one of the Himalayans used. Heterozygous D (Dd) with homo- 

 zygous E (EE) gives agouti-black; homozygous D (DD) causes the animal to be füll 

 black, and the same is the case if both D and E are heterozygous. Blacks caused 

 by the addition of D to rabbits beariiig A (agouti factor) are thus either DdEeA, 

 DDEeA, DDEEA, A being either homo- or heterozygous. These blacks, though 

 different in Constitution from blacks of the Constitution ddEEaa, are not visibly 

 distinguishable; they were discovered by the fact that black X black gave agouti 

 offspring. By mating these blacks with yellows and tortoises, it was found that 

 no agouti young were produced among 26 off spring, so proving that the factors 

 D and E show close gametic coupling. In addition it was shown that a series of 

 forms in which the black factor is replaced by chocolate can be made, and that 

 the dark pigment in the Himalayan pattern may be black, chocolate, agouti, or 

 yellow. The Himalayan pattern is recessive to self-colour; it may be combined 

 with the "Dutch" pattern giving the so-called "Mosaics" described by Castle. 



Doncaster (Cambridge). 



439) Arkell, T. B., Some Data on the Inheritance of Horns in Sheep. 

 In: New Hampshire Agr. Expt. Stat. Bulletin, 160, S. 1—35, Tables I— XV, 

 1912. 



This paper gives the results of a study of the inheritance of horns in crossses 

 involving chiefly the following breeds of sheep: Dorset Hörn, -Southdown and 

 Merino. It is held that horns in sheep represent a typical sex-limited character. 

 The male is assumed to be heterozygous (simplex) in sex, while the female is 

 duplex. An Inhibitor to hörn formation is located in the sex chromosome. There 

 are held to be two sorts of hörn determiners : a strong determiner (H) leading 

 to the Dorset Hörn type of hörn and a weak (H') leading to the Rambouillet 

 type of hörn. A Single dose of the Inhibitor does not prevent the development 

 of either type of hörn determiner, whether the latter is present in homozygous 

 form. Two doses of the inhibitor prevents the development of the hörn in hetero- 

 zygotes (Hh on H'h) but not in homozygotes (HH and H'H'). The hypothesis 

 is stated to cover all the experimental facts. The potency of hornproduction in 

 the d' may be raised by an internal secretion from the testis, but maleness can 

 only act as a stimulating influence, giving impetus to corporeal hörn growth, 

 when the determiner for hörn is present. The weak determiner, H', upon the 

 removal of this impetus may not be able to develop whatever; but H will always 

 produce horns in the soma, al though castration will lessen its potency, so that 

 a smaller hörn results. It is obvious that the determiner for hörn must always 

 be present in the germ plasm before a hörn can appear. Where it is absent in 

 both sexes (the recessive condition) the offspring will under all conditions be 

 hornless; for two recessives can produce nothing but the recessive condition. 



Pearl (Orono). 



440) Jordan, H. E., Tlie inheritance of skin color. In: Science N. S., 

 36, 918, S. 151—952, 1912. 



Die Annahme, daß dieMulatten im Gegensatz zur Mendel sehen Spaltungsregel 



