triangular glandular patch." In a recent discussion of the whole question of phosphorescence in marine organisms, Dr. Doflein concludes that the part it plays in the life of the animal probably differs in the different cases. In some it may serve to attract prey, as moths are attracted to a candle; in others it may help individuals of the same species to keep together in a swarm or to find their mates, the varying arrangement of the photophores producing characteristic light-patterns that serve as "recognition marks" like the colour-patterns of animals that live in the light of day. The clouds of luminous secretion thrown out by _Heterocarpus_ and other Prawns, and by certain Mysidacea and Ostracods, may serve to baffle pursuers, like the cloud of ink thrown out by a Cuttlefish, and in some cases the more complex organs may illuminate objects within the range of vision. That this does not exhaust the possibilities of speculation on the subject, however, is shown by the case of certain deep-sea Prawns which have been recently discovered to possess photophores placed so as to illuminate the interior of the gill cavities. What function they can discharge in this position seems beyond conjecture. The colours of deep-sea Crustacea are very curious. Few of them have the blanched appearance common, for instance, in animals that live in the darkness of caves; on the contrary, their colours are often very vivid, but they are nearly always uniform, without spots or markings, and in a large proportion of cases are in some shade of red or orange. This red colour seems to be associated, in some way that we do not understand, with the darkness of their habitat. The general absence of markings is very striking. Dr. Alcock remarks that in deep-sea Crustacea we never see "those freaks of colour, or those labyrinthine mottlings and dapplings, that excite our curiosity when handling the Crabs and Shrimps of the reefs." Possibly the explanation of this may be that in these dwellers in darkness colour is merely, as it were, an accident, a by-product of physiological processes directed to other ends, not a character of protective or warning value, as in animals that hunt and are hunted in the light of day. It is a curious fact, which may have some bearing on this problem, that in many cases, while the adults are coloured in some shade of red, the eggs carried by the female are bright blue or green.