164 THE STORY OF FISH LIFE. 



attempt to profit thereby, is in hourly danger of 

 being hoist by his own petard ! Possibly this 

 occasionally does happen. As a rule, however, 

 it is probable a catastrophe of this kind is 

 avoided by the fact that together with these 

 luminous organs has grown up a wonderfully 

 delicate sense of touch and approaching danger. 

 This new safeguard has been formed, either 

 by exceedingly long and delicate filaments pro- 

 duced by the excessive development of the 

 fin-rays, and which act like the vibrissas of the 

 cat: or as "beards" and "barbules" developed 

 round the mouth. In addition it is not improb- 

 able that these fishes have developed a sense of 

 size by which they may judge the measure of 

 approaching animals, just as we ourselves can 

 tell when in the dark that we are approaching 

 some larger body before we actually touch it. 

 Should danger be at hand the lights would be 

 dulled, or even extinguished, and in a few 

 moments escape would have been effected. 



This replacement of the eye by luminous 

 organs is another instance of the "Substitu- 

 tion of Organs." 



The enormous eyes of the fishes which see are 

 the result of selection and adaptation to the 

 requirements of the new light — the light given 

 off by the numerous phosphorescent animals. 

 A large proportion of the worms, polyps and 

 star-fish, for instance, are also phosphorescent, 

 some of them highly so. Thus Professor 

 Wyville Thomson remarks of a phosphorescent 

 brittle-star (one of the Echinoderma), that the 

 light was of a brilliant green, corruscating from 



