Studies on the Onychophora

All terrestrial animals have to solve the problem of resistance to desiccation, and adaptations associated with this difficulty are of two main types: (1) the development of waterproof external surfaces, and (2) the reduction of the amount of water lost by excretion. In some animals there is also an increase in the formation of metabolic water. In a previous paper it has been shown that the second method has been employed by the Onychophora (Manton& Heatley, 1937). A uricotelic metabolism has been acquired, and nitrogenous excretion by the intestine has reduced the water passing out by the segmental excretory organs to a minimum. The presence of large fat stores in the body may indicate that a fatty metabolism is also increasing the production of metabolic water.