Studies on photophores in the Euphausiacea

The present investigation concerns the adult morphology and histology of the photophores of some euphausiids and some notes on the development of the abdominal photophores of Meganyctiphanes norvegica. Some of the more important results are abstracted. The posterior cell mass inside the reflector layer is more complicated than earlier believed. It is composed of three or four kinds of cells. The posterior cell mass is well supplied with blood vessels and nerves. The capillaries open at the level of the inner surface of the posterior cell mass around the rod mass. The cuff-like formation of the mouth of each capillary seems to be a sphincter or an annular muscle. The nerve branches pierce the posterior cell mass and run in spirals round the capillaries, terminating on the above-mentioned cuff-like formations. The rod mass is composed of rods of different lengths. The earliest development of the abdominal photophores of Meganyctiphanes norvegica has been studied to a great extent at the larval stage of Furcilia II. The organ anlage at an early stage is composed of two anlage parts: 1) an ectodermal thickening in structural continuity with surrounding ectoderm, covered dorsally by 2) a hood-like formation of oblong cells derived from a subepidermic layer. The gradual development and the differentiations, especially of the internal structures up to and including Furcilia V, have been investigated.