In Fig. L 3b both males and females are liable to the disease, and either parent may transmit it, although descent is more often through mother than father. The movements of the eyes are very often accompanied by rhythmical movements of the head in the non-sex-limited type (Fig. L 3b), but head movements very seldom occur in the male-limited type (Fig. L 3a). In both types many of those affected have also optical defects of the eyes, especially astigmatism. No mental or nerve complications in either kind. _Key_. [M-] and [F-] male and female with Nystagmus. Otherwise as for L 1. [Sidenote: L 4] Pedigree of +hereditary Cataract+. The cataract in this genealogy begins in childhood, and usually progresses so as to require operation by the time its subject is grown up; results of operation usually good and lasting. Most of the affected members still living; of the four dead, none died before 54, and two of them lived to 78 and 83 respectively. Both sexes affected and either sex may transmit. No other eye disease and no prevalent constitutional diseases or degeneracies in the cataractous stock. Many similar pedigrees are known. _Key_. [M-] and [F-] male and female with cataract. Otherwise as for L 1. [Sidenote: M] Exhibited by Professor R. C. Punnett, F.R.S. Mendelian Inheritance in Rabbits. [Sidenote: M 1.] Yellow Himalayan Dutch × (Black) | F_{1} Agouti (reversion to wild colour). | F | ______________________|__________________________ | | | | | Agouti Black Yellow Tortoise Himalayan +Ratio.+ 27 9 9 3 16 Factors concerned:-- +A+. the factor for agouti which turns a black into an agouti, or a tortoise into a yellow. +E+. the factor for extension of pigment which when present turns a yellow into an agouti, or a tortoise into a black. +S+. the factor for self colour which turns a Himalayan into a self coloured animal. All the rabbits in this experiment contain the factor for black (B). [Sidenote: M 2.] The Himalayan pattern can occur in all four colour classes. Thus the agouti Himalayan has lighter points than the black Himalayan. (cf. 2 specimens shown.) Experiments to demonstrate that +black rabbits may be of different constitution genetically+. Factors concerned in these experiments are:-- +A+. the agouti factor. +E+. the factor for extension of pigment. +D+. a factor for density of pigmentation. All the rabbits are homozygous for the black factor +B+. Homozygous agouti = +AA BB EE+. Black rabbits may be either:-- (1) Rabbits of the constitution +aa BB EE+. These breed true and behave as simple recessive to agouti.