Fine structure of the dogfish egg case: A unique collagenous material

The fine structure of the dogfish egg case is described with special reference to the highly ordered, unique, collagen-containing fibrils. The outer layer of the case wall contains densely packed, amorphous granules, rich in tyrosine while approximately 98% of the thickness of the case is built up from orthogonally stacked laminae of closely packed, collagen-containing fibrils. These fibrils show a paracrystalline three-dimensional construction. A model for the structure of the B band of the fibril is proposed, based on appearances in transverse sections of different thickness and on two projections seen in longitudinal sections. The transverse projection of the unit cell appears to be a square lattice with sides approximately 110 Å possibly containing a pseudocell with sides $\text{110}\text{4}$ Å. The structure of these fibrils is discussed in relation to those of rat tail tendon collagen.