LIGHT BY LIVING ORGANISMS—McDERMOTT. 857 
The luminous organs of Phengodes laticollis (female) present a 
different structure. The photogenic tissue does not show the definite 
and more or less regular boundaries seen in the other species studied, 
but seems to be simply small masses of tissue, without regular margins; 
the urate layer, moreover, appears to be entirely absent. As com- 
pared with the tissues of the Lampyride above described, the indi- 
vidual cells are very much smaller, and the number of trachez is 
much less. At this time nothing can be said regarding the arrange- 
ment and distribution of the tracheal capillaries, except that only a 
very few have been observed and none could be traced to points of 
anastomosis. 
Among the other luminous organisms, considerable attention has 
been directed to the fish, the sea-stars (Ophurians), the Annelids 
(Odontosyllis) and Achole, and to a variety of other marine forms. 
Much of the more recent work is contained in Mangold’s monograph, 
and treated therein quite exhaustively. Briefly, many of the photo- 
genic organs in marine forms appear to be typically gladular, and of 
degrees of complexity varying from simple secreting cells to complex 
arrangements of glands, reflectors, and lenses. 
Piitter (@°) has divided biophotogenicity into intra- and extra- 
glandular processes and into intra- and extra-cellular luminescence. 
Under this classification the process in the fire-flies, the fish investi- 
gated by Steche (°), etc., is intra-glandular and intra-cellular. In the 
cephalopods and certain fish which are supposed to secrete a photo- 
genic product in one portion of the organ and then utilize it in another 
portion serving as a receptacle, the process is intra-glandular and 
extra-cellular, while in the annelids (Odontosyllids) [Galloway and 
Welch (*%)], Achole [Kutschera (’)], the myriapods [Dubois (>), 
Thomas (*) and others], certain prawns [Alcock (*)], and some species 
of cephalopods [Hoyle (*)], the process is extra-glandular and extra- 
cellular. (‘‘Intra-” and ‘‘extra-organic’’ would perhaps be better 
general words than intra- and extra-glandular.) 
The photogenic organs of some fish and cephalopods show a net- 
_ work of blood vessels, corresponding roughly to the aerophore trache- 
oles of the fire-flies. Many of the organs in these forms and in certain 
crustaceans (see Mangold), show a ‘‘search-light” or ‘“‘bull’s-eye”’ 
structure in which there is more or less well-defined lens, a light- 
producing body, and a reflecting layer of approximately parabolic 
outline. 
There is a considerable field for further investigation in this matter 
of the structure of the light-giving organs of different forms, and some 
of the work that has been done is in need of confirmation. We can 
not but wonder at the processes which during the ages have operated 
to produce these structures in present-day organisms—how they 
