1887.] Mr J. T. Cunningham on Nyctiphanes norvegica. 353 
means of the shrimp trawl worked a little above the bottom. We 
kept the animals alive in the “ Ark ” at Millport, and there made 
observations and experiments on the luminous organs in the fresh 
state. Their structure was investigated by Mr Yallentin, by means 
of the preserved material, at the Granton Laboratory of the Scottish 
Marine Station. 
The distribution of the organs in the body has been completely 
described by Sars. There are three pairs and four median single. 
The first pair are in the eye peduncles immediately behind and 
dorsal to the eyes. The 2nd pair are in the basal joints of 
the 2nd pair of thoracic appendages, and each of these is on the 
internal side looking towards the median line of the body. The 
3rd pair are in the basal joints of the 7th pair of thoracic appen- 
dages; each is on the external side, and looks backwards and 
outwards. Of the four unpaired organs, one is in the middle of the 
ventral surface of each of the first four abdominal somites. 
All the organs except the pair in the eye peduncles are perfectly 
similar in structure. The organ forms a spherical body lying 
immediately beneath the epidermis, and almost entirely independent 
of the surrounding tissues. The envelope of the posterior half of 
the organ is formed by a hemispherical cup of considerable thick- 
ness, of laminated or stratified structure, appearing fibrous in section, 
and non-cellular. Internal to this is a cellular layer, consisting of 
large cubical cells to the exterior, and smaller cells at the internal 
surface. The hollow of the hemisphere within this layer is entirely 
filled with a non-nucleated fibrous mass, the fibres or rods being 
externally perpendicular to the surface of the cellular layer, but in 
the centre crossing one another at right angles. In front of this 
fibrous mass is a lens of perfectly homogeneous and highly refract- 
ing substance. This is surrounded and clasped by a ring of a 
structure similar to that of the stratified layer. Outside the fibrous 
ring and the lens is a cellular layer, whose nucleated cells are smaller 
in size than those of the posterior cellular layer. Outside the 
posterior half of the organ, forming a thin mosaic-like epithelium 
over the stratified layer, is a coating of flat polygonal red pigment 
cells, which are a specialised set of the red mesoblastic cliromato- 
phores which occur beneath the epidermis in various parts of the 
body. Cellular strands may be occasionally detected passing from 
