272 THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [VI, III

they can be put in a series according to the rate and extent to which these propor-
tions are developed. A beef Shorthorn bull 14 months old is as well developed
in its proportions for meat as an adult Friesian bull 5½ years old, and the extent
to which it develops eventually is far in excess of anything found in the dairy
breeds. The directive influence of man's selection is seen in the way in which
stocks having a different origin—such as the Aberdeen-Angus and the Shorthorn—
approach one another in conformation for beef purposes (and Friesians and Dairy
Shorthorns for milk purposes), whilst stocks with a common origin—such as
the Shorthorn—have developed different types when bred for different purposes,
such as beef and milk (see Plate XVI).

Of quite another nature genetically, and in no way dependent on environ-
mental and nutritional conditions, is the ' Doppellender' calf, which is so much
valued for veal on the Continent (Fig. 4, Pl. XVII). It consists of a doubling of
the muscles of the loin and hind quarters, and has arisen as a mutation in
several Continental breeds of cattle, in which it is carried on in the heterozygous
condition, for the females are sterile. It is a simple recessive and forms no
blend in crossing as do the developmental characters. It cannot, therefore, be
used to improve other stocks in the same way that Aberdeen-Angus bulls are
used to introduce an improved conformation and better quality when mated to
coarse-boned and ill-proportioned cows.

The colour of the body-fat in cattle is a multiple-factor genetic
character; all shades of colour exist from a very pale yellow (which is
desired by the butcher) to a deep yellow (which is desired by the breeder of dairy
cattle). The expression of this character is dependent on the amount of the
xanthophyll pigments of plants in the food, and if these are absent the fat becomes
white, no matter what the genetic constitution is. In selecting for this character
the breeders of dairy cattle feed plenty of greenstuff and pick out those cows
which give the deepest yellow tint. Variability curves (by Whetham) for the
colour of the butter-fat in the different breeds of cattle at the London Dairy Show
are shown in the next figure (Fig. 5, p. 274). This is a case where a definite envi-
ronment of food-supply is necessary before selection can be made for the genetic
character concerned.

Sheep (mutton and lamb).—As with beef, the genetic characters for mutton
and lamb are all ' developmental' ones, and in Great Britain there exists a com-
plete range of types from those possessing early maturing qualities (that is, a quick
change in the proportions of the body), and suitable for killing as lamb, to those
with a slow change in proportions, which are more suited to mutton-production.
These characters are not firmly fixed, however, and may be modified in any one
breed by the methods of feeding and management adopted. During growth, the
tissues of the body develop in a definite order—bone, muscle, and then fat. The
proportional development of these tissues varies considerably in different breeds;