SHEEP.--REMARKABLE RACES OF--VARIATIONS ATTACHED TO THE MALE SEX--ADAPTATIONS TO VARIOUS CONDITIONS--GESTATION OF--CHANGES IN THE WOOL--SEMI-MONSTROUS BREEDS. GOATS.--REMARKABLE VARIATIONS OF. The breeds of the pig have recently been more closely studied, though much still remains to be done, than those of almost any other domesticated animal. This has been effected by Hermann von Nathusius in two admirable works, especially in the later one on the Skulls of the several races, and by Rütimeyer in his celebrated Fauna of the ancient Swiss lake-dwellings.[144] Nathusius has shown that all the known breeds may be divided in two great groups: one resembling in all important respects and no doubt descended from the common wild boar; so that this may be called the _Sus scrofa_ group. The other group differs in several important and constant osteological characters; its wild parent-form is unknown; the name given to it by Nathusius, according to the law of priority, is _Sus Indica_ of Pallas. This name must now be followed, though an unfortunate one, as the wild aboriginal does not inhabit India, and the best-known domesticated breeds have been imported from Siam and China. {66} Firstly, the _Sus scrofa_ breeds, or those resembling the common wild boar. These still exist, according to Nathusius (Schweineschädel, s. 75), in various parts of central and northern Europe; formerly every kingdom,[145] and almost every province in Britain, possessed its own native breed; but these are now everywhere rapidly disappearing, being replaced by improved breeds crossed with the _S. Indica_ form. The skull in the breeds of the _S. scrofa_ type resembles, in all important respects, that of the European wild boar; but it has become (Schweineschädel, s. 63-68) higher and broader relatively to its length; and the hinder part is more upright. The differences, however, are all variable in degree. The breeds which thus resemble _S. scrofa_ in their essential skull-characters differ conspicuously from each other in other respects, as in the length of the ears and legs, curvature of the ribs, colour, hairiness, size and proportions of the body.