Observations on the comparative morphology and operation of the photogenic tissues of myctophid fishes

Lanternfishes (Myctophidae) often bear not only small primary photophores, but also larger regions of luminous tissue, described as glands or patches. These have a superficial appearance very different to that of the primary photophores, but examination of the tissues of some 14 genera has shown that all the luminous organs are composed of fundamentally similar stacks of photogenic lamellae. The degree of organisation of the lamellae varies in different genera, but the caudal organs and the other larger luminous regions contain much more of this photogenic tissue than do the primary photophores. Some observations on the operation of both primary and caudal organs are described.