1. The development of the polymorphonuclear leucocyte from a mesenchymal, lymphoid type of cell is possible in adult life and in vitro in chicken bone marrow.

2. These cells can rapidly proliferate by means of amitotic division of an unripe form very similar to, but smaller than themselves.

3. All the cells of chicken bone marrow can undergo a transformation to a type of cell resembling, although not proved to be identical with the cells of connective tissue.

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