The fine structure and biology of the egg-shell of the wheat bulb fly, Leptohylemyia coarctata

Abstract

ABSTRACT The egg-shell of Leptohylemyia coarctata consists of 3 meshwork layers. The outermost wall is a sheet with perforations that are usually 5 to 10 μ wide. Across each of these perforations is a very fine network, the interstices of which are 0·1 to 0·2 μ wide. The middle meshwork layer is 2 to 7 μ thick. It is chiefly responsible for the mechanical strength of the shell. The inner meshwork layer is usually 2 to 4 μ thick. It consists of vertical columns extending inwards from the middle layer. The apices of the columns are branched in a plane normal to their long axes. These horizontal branches anastomose to form an open network, which is the innermost wall of the shell. The struts of all meshworks consist of fibrils 1 to 1·5 mμ · in diameter. The fibrils form a meshwork, the interstices of which are usually 2 to 5 m μ · wide. When the egg is submerged in water, a film of air is held by the hydrofuge inner meshwork. This film of air functions as a plastron, but as a relatively inefficient one because above it there is a stationary layer of water 8 to 15 · thick held by the 2 upper meshwork layers, which are hydrophil. Between the shell and the subchoral cuticle there is a waxy membrane. This membrane is closely attached to the inner face of the shell. It plays an important part in the resistance of the egg to desiccation.