TISSUES OF LIGHT-PRODUCTION 129 



seen in our section to be of a poor shape to reflect the lateral rays and 

 those lost in the central part of the apparatus. 



In the space between the pigment and reflectors is a connective tissue 

 of unknown function. Also in the small space that lies within the arms 

 of the reflectors we see another and somewhat fibrous connective tissue 

 instead of the photogenetic cells as in most organs similar to this one. 



The light-producing cells form a disk-like mass, somewhat thickened 

 and very slightly concave on the distal surface. The cells themselves 

 are not arranged in columnar order as in the last specimen, but are packed 

 together in several thicknesses with vacuole-like spaces in the mass. 

 The nuclei are branched and large. Cell boundaries are entirely wanting. 



In the front of the light-cell mass comes the lens. It is of the same 

 shape (a disk) as the light-cell mass, but nearly four times as thick in 

 the proximo-distad direction. Its proximal surface is slightly convex 

 to fit the concave surface of the light mass, and its anterior surface is 

 the same shape to agree with the contour of the entire sac, against whose 

 wall it lies. Its substance is made up of fibrous or plate-like cells packed 

 in bundles, all of which lie at right angles to the axis and to the light rays. 

 The nuclei are small and scattered. 



A circular ring of reticular connective tissue surrounds the lens on 

 all sides. It is about as thick as the lens mass, and taken together with 

 it, forms a large disk, which occupies the front or distal part of the eye. 

 The lens does not touch the actual body surface, but between it and the 

 thin, tough cornea is a space, probably to contain a fluid. 



Several Worms possess a Fairly Strong and Steady Luminosity. One 

 marine Annelid gives a bright spark during the mating season. An 

 earthworm shows a general light given off in the slime, as is done in Pholas. 



Light-organs are rare among the Crustacea, but are of interest because 

 of the relationship of their bearers to the insects. Some Copepoda show 

 a luminosity which is produced by granules of a secreted material that 

 is thrown off. Woltereck has mentioned a possible case among the 

 Crustacea in the deep-sea Amphipod,Scypholanceola, which has two pairs 

 of peculiar organs on the head. No adequate description of the histology 

 of these organs was accessible to the writers. 



The best case of luminosity in a Crustacean is that of the Schyzopod 

 group, Euphusida, a pelagic family with many representatives. The 

 organ, as found in the form Nyctiphanes Norvegica, has been described 

 by Vallentin and Cunningham as well as discussed by Giesbrecht,and we 

 shall use it as a type. The light-organs, or photos pheria, of this animal 

 show two forms. That found on the eye pedicle is not as well developed 

 as those found along the sides of the body. The one found on the side 

 of the first abdominal segment is characteristic and fully developed. It 

 is complex and highly efficient (Fig. 119). 



