The feeding mechanism of the nudibranch Calma glaucoides (Alder & Hancock) has been described by Evans (1922) and that of the crustacean Nebaliopsis typica (Sars) by Cannon (1931) and myself (1943). Calma is seasonally relatively abundant in the coastal waters of parts of Europe where it is found attached to the eggs of certain fishes. It is known to feed exclusively on these eggs and young embryos. Nebaliopsis is a deep pelagic form from the Antarctic Ocean. It has been obtained only rarely and cannot be observed alive and in its natural environment. Two specimens were available for examination. Thus complete certainty about the diet is impossible. The external features and mouth parts were described by Cannon and the structure of these suggested that Nebaliopsis, like other known Nebaliacea, might be a filter feeder. Examination of the morphology of the gut and its contents indicates that this is very improbable. There is no mechanism for the sorting out of particles of different sizes such as is found in other filter feeders. The food passes into a blind sac and there is no apparent means by which the large quantities of indigestible material taken in when particles are filtered from the water indiscriminately might be evacuated. In addition to this negative evidence the food mass found in the large storage chamber of one specimen was completely homogeneous and structureless, its appearance in section suggesting coagulated yolk. It has therefore been suggested that Nebaliopsis feeds on fish eggs found floating in the deeper water layers.