TEGUMENTAL GLANDS AND TERRESTRIAL LIFE IN WOODLICE

Abstract

SUMMARY The lobed tegumental glands would seem to play an important part in adapting woodlice to life on land, but although the problem seems a simple one, it has by no means been easy to determine their function. Evidence from comparative anatomy and physiology is unhelpful and often puzzling, and inactivating the glands seems to have no effect on normal life. Evidence from a more direct experimental investigation of a variety of hypotheses suggests that the glands do not perform any of the more obviously possible functions, and that they are not concerned with general defence, secretion of gill fluid, water‐proofing the body‐wall, attachment to the substratum, moulting, lubrication of the skin, reproduction, silk formation, capillary water conduction to the gills, temperature control, humidity reactions, or regulation of water content of the body. Evidence of various kinds suggests that the function performed by the glands is that of defence, not against predators in general, but against one particular group, namely spiders. Spiders appear to be potentially the most serious enemies of woodlice; but they find woodlice distasteful and the degree of distastefulness is correlated to a remarkable extent with the degree of development of the lobed glands. There is other evidence that the distastefulness is a property of the lobed gland secretions and not of the body tissues and fluids as a whole. When a woodlouse is attacked by a spider, its lobed glands secrete precisely as they do when stimulated experimentally, and this is the only evidence ever obtained of secretion occurring under natural conditions. If the function of the lobed glands is to repel spiders, many of the objections to the general defence hypothesis can be answered, and many other puzzling facts relating either to the glands or to the behaviour of woodlice can be explained.