1. The positions of degenerating cells in the mesenchyme of the scleral bone primordia of the chick, and in the fibrous sclera beneath them, have been ascertained.
2. It is shown that the number of cell deaths within the bone primordia, and also beneath them in the fibrous sclera, is markedly higher than, and follows a different pattern from the regions between.
3. A centre of cell destruction is seen to occur at and near to the boundary of the mesenchyme and fibrous sclera. This begins in 7- to 8-day primordia, rises to a peak at 8 to 9 days, and subsides in 9- to 10-day primordia.
4. A second centre of cell death occurs in the mesenchyme nearer to the conjunctival papilla. It starts in 8- to 9-day eyes about mid-way between the conjunctiva and sclera, and as it increases in intensity, the centre moves nearer to the conjunctival papilla (9 to 10 days), beneath which it appears to subside (some 10-day primordia).
5. The function of these waves of cell destruction is discussed. It is concluded that their most likely function is morphogenetic; they may make a space into which the osteogenic cells migrate, or they may ensure a normal position and shape for the developing bone. Consideration has also been given to the possibility that the products of cell death might have a histiogenetic function.
