622 THE BIOLOGY OF MARINE ANIMALS 



rondeletii, S. birostrata, Loligo edulis and others. The accessory organs 

 open into the mantle cavity, and in S. birostrata a luminous secretion is 

 actually discharged, but not in S. rondeletii. It has already been pointed 

 out that some individuals of a species only are luminous, and sexual diff- 

 ences also occur: in Rossia and Sepietta, for example, accessory glands 

 are confined to the female, whereas in Sepiola they are present in both 

 sexes. 



Luminous bacteria have been isolated from various myopsid squid and 

 have been cultured. Special growth characteristics and luminous reactions 

 have been ascertained, which indicate close adjustments to particular 

 hosts, but Kishitani also discovered so-called symbiotic species living as 

 saprophytes on the inner mantle surface. According to Herfurth (43), the 

 bacteria are not transmitted from one generation to another through the 

 egg, and each generation must be reinfected anew. Consequently it is by 

 no means certain that a true symbiotic relationship is involved, and the 

 biological significance of luminescence in these animals is most obscure 

 (12, 42). 



The luminous test cells which lie at the entrance of the branchial 

 chamber of Pyrosoma contain convoluted tubular bodies with an internal 

 granular reticulum (Fig. 13.15). These have been regarded as bac- 

 terial bodies which reproduce by spore formation and infect the next 

 generation through those test cells which invade the developing embryo 

 (12). There are, however, certain cogent reasons for taking exception to 

 this interpretation. It has been observed that luminescence in Pyrosoma 

 is discontinuous and appears only after stimulation of the animal. The 

 luminescent material can be dried, and caused to lighten by the addition 

 of fresh water. Finally, potassium cyanide, which depresses luminescence 

 in bacteria, is without effect on the luminescence of Pyrosoma. It would 

 appear, then, that the production of light may be an intrinsic characteristic 

 of this animal (42). 



Symbiotic relationships with luminescent bacteria are frequent among 

 marine teleosts, and the light-organs concerned are diverse and frequently 

 very complex (p. 559). The bacteria lie in epithelial tubes or folds, and in 

 the anomalopids, for example, the light-organ is made up of rows of 

 epithelial tubules containing rod-like bacteria, and possesses a well- 

 developed vascular supply. The bacteria have been cultured in some in- 

 stances, but little is known of the development of the relationship. In all 

 these forms light is emitted continuously by the symbiotic bacteria. In 

 some species, e.g. the macrourid Malacocephalus, a luminous material 

 can be extruded from the gland (Fig. 13.22). Frequently, the fish is able 

 to control the actual emission by means of screening devices, e.g. Photo- 

 blepharon. 



Some instances of luminescence have been described in which the light 

 is due not to symbiosis but to an attack by pathogenic luminescent 

 bacteria. In the amphipod TaJitrus a. small proportion of individuals are 

 luminescent and so infected, and the disease eventually leads to the death 



