No abstract

Recent studies of the cephalic glands of Campodea have shown previous descriptions to be misleading in several respects. The campodeid salivary glands lie in the posterolateral parts of the head capsule and each is composed of a much-coiled ‘labyrinth’ and a distal end-sac. The histology of the two regions differs greatly, and although a little secretory activity has been observed in the end-sac, the labyrinth appears to be responsible for secreting most of the definitive saliva. The latter is passed to the outside down a median duct which opens between the ‘setigerous plates’ of the labium. Although the salivary glands of Campodea have homologues in other apterygote insects and the myriapods, the homology of the second pair of cephalic organs, the lobulate glands, is obscure. These glands, which are situated in the head and the anterior part of the prothorax, are composed of cells arranged around a system of ducts opening into the cephalic haemocoel. The ducts contain acidophil material which is secreted by the gland cells and numerous small cells which are perhaps haemocytes. The size of the lobulate glands relative to the size of the body increases as the animal matures, and it is possible that they are responsible for secreting some form of growth hormone. The cheek glands are situated beneath the epidermis of the lateral part of the head capsule and are composed of two different types of cells; their homology and function are unknown. The paired lateral sense-organs also lie beneath the cephalic epidermis, but each is a bowl-shaped structure composed of numerous bifid sensory cells. The latter are innervated and each contains a bifid sensory rod. The distal prolongations of the sensory cells are interpolated between accessory cells whose cytoplasm contains granules. The latter may be either proximally or distally situated in the cell but are not composed of pigment. The definitive structure of these senseorgans is only attained in the sexually mature insect and they are only represented by disorganized groups of cells in the nymphs. Preliminary experiments are described which indicate that the lateral sense-organs are not concerned with the perception of optical stimuli and their function and similarities to other insect sense-organs are discussed.