By Roy Robinson and G. A. Kerkut (Auth.)
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This infers that the genetic action is not constant throughout the scale and a scale transformation is necessary as a counterbalance. One common feature of the damping is the difficulty which is experienced in eliminating the final small spots of colour or of white in selection studies. This could be interpreted as an exhaustion of the underlying genetic variability; whereas this is not necessarily so, the phenomenon being rather a facet of the normal expression of this type of character. A cross was performed between the minus and plus lines after 6 and 5 generations of selection, respectively.
The general pattern was that of parallel lines of follicles with the groups of one line alternating with the groups in adjoining lines. The soles of the feet were devoid of hair but the dorsal parts were thinly covered with soft fibres. The tip of the scrotum was covered with only short fine hairs. The fibres on the tail were reduced to short bristles arising from under the edge of each scale. The long vibrissae emerged in 5 or 6 parallel rows extending from the nose backwards along the upper lip.
On the belly there were roughly equal numbers of adjacent and associate groups but on the back there were almost twice as many of the latter as the former. The average number of follicles in an adjacent group was 5 for the dorsum and 6 for the venter. The number in an associate was more constant, being about four for both surfaces of the body. Table 4 shows the average number of hairs, follicles and groups per square millimetre of skin surface (dorsum and venter) in 3 to 10 mm 2 , respectively, in four animals.