You will be shown an abstract from a biomedical research paper. Given this abstract, your task is to extract all unique entities of the following types: ["AnatomicalEntity"].

Please return the output as a JSON object of the format: {"AnatomicalEntity": ["tumor cells", ...]}. The keys should be entity types and values should be lists of extracted entities belonging to the corresponding type. If you cannot find entities belonging to a specific type, the value should be [].

Only output the JSON object and do not include any additional text.

Abstract:

The patterns of internal migration in Maharashtra:  an analysis of 1971 census data.
Patterns of internal migration in the state of Maharashtra, India, for the period 1961-1971 are analyzed using 1971 census data.  The nature, volume, and direction of migration are examined.  Migrants are characterized according to factors including age, sex, marital status, occupation, and areas of origin and destination.
{"AnatomicalEntity": []}