Hereditary Diseases of Sheep and Pigs. 
17 
physical and mental, healthy and diseased. In obedience to this 
natural law the grain of wheat, when placed in the soil, shoots 
up its cfrassy stem, and bears numerous grains resembling the 
parent seed. The seed which falls from the forest tree produces 
a tree like that which yielded it, and every flower and herb 
reproduces its own kind and no other. Throughout the animal 
kingdom the same law also regulates the transmission from the 
parent to the offspring of salient qualities, whether good or bad, 
external or internal. But to examine somewhat more fully these 
interesting topics, and to illustrate more satisfactorily the subject 
of this Report, we shall notice briefly some of the more important 
hereditary qualities of sheep and pigs. 
The numerous varieties of the human race, as well as of every 
species of the lower animals, are doubtless due to the modifying 
influence of external circumstances, and the perpetuation of 
acquired distinctive peculiarities. We must therefore attribute 
the existence of the many varieties of sheep which are found in 
the world, to the hereditary transmission of distinctions originally, 
either mere lusus nuturcE, or the ordinary modifications induced 
by climate and other external circumstances. Our English 
Leicester and Southdown, our Scotch black-face, the Argali of 
Siberian Kamschatka, the fat-tailed sheep of Syria and Barbary — 
in short, all the existing varieties of sheep, however distinctive 
their present characteristics, have had one common origin, and 
have become distinct breeds only by the hereditary transmission 
of acquired peculiarities. Of course to form varieties differing 
so widely in external form and in habits, has required the lapse 
of thousands of years ; but in illustration of the principle, and 
as an instance of the transmission of acquired characteristics, 
forming a distinct variety in a comparatively short time, we 
may adduce the breed of sheep now found in Massachusetts, dis- 
tinguished by an otter-like form, long body and short and crooked 
legs. This breed had its origin in 1791 with a male lamb born 
with these peculiarities, which, although at first merely accidental, 
have, by continual care and cautious breeding, been rendered 
permanently hereditary. The variety is highly prized on account 
of its being easily kept within fences.* 
But it is not the distinctive characteristics of different breeds 
that are alone transmitted from parent to offspring. Different 
families of the same breed are often characterised by hereditary 
distinctions, such as peculiar colours and markings ; indeed 
almost every sheep-owner must be able to recollect instances of 
particular families distinguished for many generations by the 
frequent appearance of individuals with black fleeces, black legs 
VOL. XVI. 
* Youatt on Sheep, p. 135. 
C 
