CHAPTER XIV 



ILLUMINATING THE OCEANS 



THERE are three main ways in which squids pro- 

 duce Hght: through bacteria in their bodies, by 

 secretion, and by means of photophores or 

 luminous organs. 



There are many squids inhabiting shallow water which 

 have luminous bacteria living in glands beneath their 

 mantles. These amazing glands have lenses and reflectors 

 and exist for the sole purpose of producing light. Each of 

 these squids has a built-in rear-hght, with a magnifying 

 optical system — and it uses Hght-producing fuel for 

 hours without need of recharging. The Japanese auth- 

 ority on luminescence, Yata Haneda, states that "the 

 light is continuous yet controlled by a thin film of ink 

 about the glands". 



Luminous bacteria are quite different from the 

 ordinary luminescent species of bacteria which live on 

 the skin of some marine animals. A creature known as 

 the lantern squid uses these bacteria, also the Spirula — a 

 cephalopod belonging to a genus having a flat spiral 

 shell in the hinder part of the body. Johannes Schmidt 

 observed a Spirula several times which emitted a pale 

 yellowish-green light. The spirula's lamp, unHke others, 

 burns continuously without fading. It is an organ which 

 has a diaphragm above it which automatically switches 

 the light on and off. 



The squid Heteroteuthis dispar is sometimes regarded as 

 a deep-sea species, but it has been brought to the surface 

 from depths of only four hundred or five hundred feet. 



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