An electron-microscope study of capsule formation by insect blood cells.

Haemocytes of Ephestia kuehmella adhere to foreign objects introduced into the haemocoel and form capsules around them. The fine structure of these capsules, and the blood cells which form them, has been studied by electron microscopy. By 72 h the capsule is a compact tissue, about 50-60 cells thick. The cells retain their integrity and do not form a syncytium. Cells nearest the implant develop large numbers of cytolysomes and appear necrotic. Peripheral to this the cells, which are initially more or less spherical and about 6 ft across, are flattened into thin sheets, on average about 0-3 fi thick. Capsule cells adhere closely to each other, and a conspicuous electron-dense material may be present between them. The structure of developing capsules 24 h old and of capsules retrieved from adult insects following metamorphosis is described. The formation of capsules is discussed in relation to general problems of cell recognition and adhesion.