SAND-HOPPERS 155 



Murray, of the " Challenger," at Millport, on the Clyde. 

 He had obtained them (the kind called Nyctiphanes) in 

 great quantities at a depth of ninety fathoms in the 

 great Scotch fiord, and amongst other curious facts 

 about them had shown that they enter Loch Fyne in 

 vast .numbers, and are the special nourishment of the 

 celebrated Loch Fyne herrings. It had been noticed 

 that the intestine of the plump, well-fed herrings is full 

 of a deep-black substance, and Sir John Murray showed 

 that this was the black, indigestible pigment of the eyes 

 of the hundreds of phosphorescent shrimps swallowed by 

 these favoured fish, which owe their fine quality to their 

 special opportunity for feeding in the depths of the loch 

 on the exceptionally abundant and nutritious light- 

 producing crustaceans ! At night my friend showed me 

 a large glass vessel holding four or five gallons, in which 

 were a hundred or so of the phosphorescent shrimps 

 swimming around. We turned out the lamps of the 

 room, and all was dark. Then a gentle tap was given 

 to the jar, and each little crustacean lit up, as though 

 by order, a row of seven minute lamps on each side of 

 its body, swimming along meanwhile, and reminding one 

 of a passenger steamer, as seen from the shore, as it 

 glides along at night with its lights showing through a 

 row of cabin windows. The shrimps' lights shone 

 steadily for a minute or so, then ceased, and had 

 to be lit up again by again signalling their owners 

 by knocking on the glass. These little lamps, with 

 their bull's-eye lenses, are far more elaborate struc- 

 tures than the glands which in other cases cause a 

 flash by discharging a luminous secretion into the water. 

 They are even more elaborate than the internal 

 permanent phosphorescent structure of the glow-worm 

 (an insect, not a crustacean), which has no condensing 

 lens. 



