PHOTOSPHERIA OF NYCT1PHANES NORVEGICA. 327 



the principal axis of the organ. The posterior part of the 

 organ is bounded by a layer composed of wavy fibres or 

 laminae, which are generally parallel in direction, but are to 

 some extent interlaced and anastomo-ed ; this layer is of con- 

 siderable thickness, and forms a hemispherical cup open in 

 front, and in front only ; it is perfectly continuous everywhere 

 behind its free edge, being pierced by no apertures whatever. 

 This is the layer called by Claus a coarse pigmented fibrous 

 membrane, and by G. O. Sars a thick elastic cuticle. The 

 layer is not pigmented except on its internal surface, which will 

 be referred to later. It is non-cellular, that is, contains no 

 nuclei nor distinguishable cell-areas. This layer resembles to 

 some extent a tapetum, and as one of its functions is un- 

 doubtedly the reflection of light from its internal surface, we 

 may adopt for it the name used for a similar layer in the phos- 

 phorescent organs of fishes by Von Lendenfeld, that of reflector. 

 Covering the exterior surface of the reflector is a flat, mosaic- 

 like epithelium of polygonal red pigment- cells. The appear- 

 ance of these, as seen after slight compression in a fresh organ, 

 is shown in fig. 2. 



Red pigment is present in patches and dots in other parts of 

 the animal's body, and is everywhere contained in stellate 

 mesoblastic chromatophores, situated close beneath the epi- 

 dermis. It is obvious that the epithelial covering of the 

 reflector is a special development of these chromatophores. 

 Where the chromatophores are not present the body of the 

 animal during life is beautifully pellucid. Internal to the 

 reflector is a layer of large cells, somewhat higher than broad, 

 and each containing a large nucleus. These cells are, in some 

 places, in two layers, though the layers are not regularly super- 

 imposed. The largest cells are near the surface of the reflector, 

 and smaller ones exist above them in some parts. The 

 internal surface of the cellular layer is perfectly smooth and 

 hemispherical in shape, and in the hollow contained by it is a 

 curious fibrillar mass. The fibrils of this mass are for the 

 most part straight, and in its external part are perpendicular 

 to the surface of the cellular layer, while the core of the mass 



