November 3, 1923] 



NATURE 



659 



develop upon the cakes serve as food for the termites. 

 (3) Ants belonging to the genus Atta cultivate fungi ; 

 the queen, when about to found a new colony, carrying 

 away a small ball of fungus wherewith to start a fresh 

 culture in the new habitat. 



Group 11.— Symbiotic organisms developing in the 

 lumen of the intestine and its adnexa. As examples may 

 be cited the bacteria occurring in the intestines of fly 

 larvae (Musca, Calliphora, etc.), which aid the larva to 

 digest meat ; the bacteria associated with the olive-fly 

 (Dacus olea) ; the Trychonymphids of xylophagous 

 Termites (Leucotermes lucifiigus). 



Group III. — Intestinal symbionts situated in the 

 epithelial cells of the digestive apparatus. In Anobiiim 

 paniceum, a small beetle commonly occurring in flour, 

 a part of its mid-gut contains cells filled with symbiotic 

 yeasts undergoing multiplication. The s}Tnbionts are 

 acquired by the larva on hatching, being eliminated 

 by the female beetle. 



Group IV. — Intracellular symbionts of deep tissues. 

 This group of symbionts is most frequently found in 

 insects, but their nature was not disclosed until recent 

 years. Thus an organ, constantly present close to the 

 ovary in Aphis, the " pseudovitellus," is now known 

 to contain symbionts, for in 1910 Pierantoni and 

 §ul? independently demonstrated that certain intra- 

 cellular inclusions were yeasts the evolution of which 

 they followed. Their results have been confirmed by 

 various authors, especially by Buchner, to whose 

 collective work on the subject most of our information 

 regarding this class of sj-mbionts is due. 



Among the symbionts of deep tissues in insects are 

 found a whole series of specialisations among the host- 

 elements harbouring the symbionts. In Lecaniinae 

 yeasts are distributed throughout the body (perivisceral 

 fluid, cells of fat-body) ; the fat-body cells may be 

 regarded here as facultative Mycetocytes. In Orthezia, 

 symbiotic bacteria occur in certain fat cells. In 

 Cicadas, yeasts occur in fat cells which continue to 

 accumulate fat, glycogen, and urates. In Blattids, 

 symbiotic bacteria are found in special cells forming 

 well - differentiated Mycetocytes. These also occur 

 about the digestive tract of Pediculidae (Hsematopinus) 

 and certain ants (Camponotus). Mycetocytes may 

 agglomerate to form true organs termed Mycetomas, 

 the component mycetocytes containing either yeasts 

 or bacteria as symbionts, as in Aphids, Chermids, and 

 Aleurodids. In Pediculus and Phthirus, parasitic on 

 man, the mycetoma is disc-shaped and lies centrally 

 as a distinct milk-white structure upon and indenting 

 the mid-gut. 



The mode of transmission of intracellular symbionts 

 of insects from generation to generation may take place 

 in differentways as defined by Buchner (192 1, somewhat 

 modified) : I. The larva of each generation infects 

 itself through the mouth (Anobiidae). II. Infection 

 takes place hereditarily through the egg. Ill, Em- 

 bryonal infection as in parthenogenetic Aphids. 



As already indicated, the symbionts may be yeasts, 

 saccharomycetes, bacteria, or even nitrobacteria. 

 Their entrance into the cells and their presence therein 

 even in large numbers docs not in many cases prevent 

 multiplication of the invaded cells or affect their 

 mitosis. 

 We know little regarding the part played by symbionts 



NO. 2818, VOL. 112] 



in insects ; our information relates almost exclusively 

 to their morphology, mode of multiplication, and entry 

 into the host during its development. There are no 

 indications that the symbionts are injurious or patho- 

 genic. We may well ask ourselves what are the 

 reciprocal advantages of this association, but this is a 

 question that it is impossible to answer in view of 

 our ignorance of physiological and biochemical processes 

 in insects. 



(3) Micro-organisms in Relation to Luminescence 

 in Animals. 



A fairly large number of organisms are known which 

 have the faculty of emitting light. They are found 

 among bacteria, fungi, protozoa, ccelenterates, echino- 

 derms, worms, molluscs, Crustacea, insecta, tunicata, 

 and fish. As a rule, luminescence in animals depends 

 upon the action of luciferase on luciferin, but recently 

 a number of cases have become known wherein light 

 production has been traced to micro-organisms, and it 

 is with these cases that we shall deal. 



Luminescent pathogenic bacteria may invade the 

 host, as described by Giard and Billet (1889-90) for 

 the small marine amphipod, Talitrus. 



Luminescent symbiotic bacteria are present in 

 luminescent organs of certain insects, cephalopods, 

 tunicates, and fishes : — 



Insects: Pierantoni (1914) found them in glow- 

 worms (Lampyrus), the luminescent cells being crowded 

 with minute bodies having bacteria-like staining 

 reactions, these bodies being also present in the beetle's 

 egg, which is luminous. 



Cephalopods : We owe to Pierantoni (1917-20) and 

 Buchner the discovery that luminescence in certain 

 Cephalopods is due to light-producing bacterial 

 symbionts living in special organs of the host. In 

 Loligo the luminous organs, known as " accessory 

 nidamentary glands," consist of epithelial tubes 

 surrounded by connective tissue. In cuttle-fish (Sepiola 

 and Rondeletia) the organs are more complicated, the 

 glands being backed by a reflector, and provided out- 

 wardly with a lens serving for the projection of the 

 hght rays generated by the symbionts within the 

 tubes. The symbionts are transmitted hereditarily 

 when the Cephalopods lay their eggs. The symbionts 

 of Loligo and Sepiola have been cultivated. 



Tunicata: In Pyrosomidae each individual in the 

 colony possesses two luminescent organs, in which 

 Buchner (1914) demonstrated symbiotic fungi that are 

 transmitted hereditarily. 



Fish : Of great interest are the researches of Harvey 

 (1922) upon light production by two species of fish 

 (Photoblcpharon and Anomalops). Their luminescent 

 organs arc composed of a great number of sets of 

 parallel gland tubes. Luminous material fills the lumen 

 of the tubes and consists of an emulsion containing 

 many granules and rods ; the latter move about with 

 a corkscrew-like motion, and are undoubtedly bacteria. 

 The luminosity of the organ is due to these symbiotic 

 bacteria. 



In concluding this section dealing with light pro- 

 duction by animals it may be repeated that we have 

 to distinguish between {a) luminescence due to symbiotic 

 organisms, such luminescence being continuous in the 

 presence of oxygen as in cultures of luminous bacteria 



