THE FINE STRUCTURE OF THE PERITROPHIC MEMBRANES OF CERTAIN INSECTS

¹ Chemical Physics Section, Division of Industrial Chemistry, C. S. I. R. O., Melbourne, Victoria, and Division of Entomology, C. S. I. R. O., Canberra, A. C. T., Australia

1. Some details of the fine structure of the peritrophic membrane of Periplaneta and of several other insects have been determined electron microscopically.

2. The membrane appears to be a complex structure of which the most characteristic and resistant component is a fibrillar network. A second component is a layer closely associated with the fibrillar network, consisting of unorganized fibrils embedded in an amorphous ground substance. The layers may be loosely associated and become separated on shaking the dissected membrane in water. The fibrils probably consist of chitin and the ground substance of protein.

3. The fibrillar network generally consists of three systems of parallel fibrillar strands placed at 60° to each other; thus it possesses hexagonal symmetry. A variety of defective arrangements, arising from mesh distortion, suppression of one set of fibrils and other grosser defects, may occur. The diameter of the fine fibrils composing the strands is about 100 Å and there may be several in each strand. The separate strands of a system of fibrils are about 0.15 to 0.2µ apart. The fibrillar networks are well adapted to the formation of tough sheets, not readily torn.

4. Membranes of this nature were also found in Locusta migratoria and Galleria mellonella.

5. The nature of these membranes suggests that they are formed by delamination from a surface. This view of the mode of formation may account for the development of the fibrillar arrangement if it is assumed that the fine fibrils are deposited from a secretion onto a surface bearing an hexagonal pattern to act as a template.