Inheritance of the first-born child ("Ane-Katoku Sozoku" in Japanese) refers to a system which stipulates that if a female happens to be the first-born child, then she (saying exactly, her adopted husband "Muko-Yoshi" in Japan) inherils the family's entire holdings. This system is different from primogeniture, in the strict sense of which the eldest son inherits the family's holdings.
The custom of the first-born child inheriting was found in the North-East Regions of Japan, and exsisted until the early days of the Meiji-period. But after that, it began to break down.
My report explains the following.
1) The actual state of this custom in Satomi-Village in Ibaragi.
2) The reason why this custom efisted.
3) The process by which this custom broke down under the influence of the Act of Conscription and the Meiji Civil Code.