LIGHT BY LIVING ORGANISMS — McDERMOTT. 357 



The luminous organs of PTiengodes 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 LampyridaB above described, the indi- 

 vidual cells are very much smaller, and the number of trachese 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 Acholce, 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. 



Putter ( 59 ) 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 ( 62 ), 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 ( 22 > 23 )], Acholm [Kutschera ( 37 )], the myriapods [Dubois ( 15 > 16 ), 

 Thomas ( 65 ) and others], certain prawns [Alcock O], and some species 

 of cephalopods [Hoyle ( 29 )], 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 



