166 MOUNTAIN AND MOORLAND 



that the adults die after spawning. We have found 

 even the big Sea Lamprey, which is as long as our 

 arm, lying spent by the side of the river, an illustra- 

 tion of the fact that the beginning of new lives is 

 often the ending of the old. But it is time we were 

 getting farther up the stream. 



Where we follow the stream upwards and turn into 

 the glen, which is at first widely open, there is on one 

 side a grassy and mossy bank which passes into a 

 pine-wood at the top. There, late in the midsummer 

 evenings, we have watched the Glow Worms flashing 

 their signals. Our stream is in the West of Scotland. 



Glow Worms (Lampyris noctiluca) are Beetles, and 

 although there is a little power of light production in 

 the eggs, the larvae, and the winged males, it is mostly 

 the wingless females that glow. These are dark, 

 flattened, short-legged, rather grublike creatures, 

 nearly half an inch long. They lie quiet during the 

 day and climb up on to the herbage in the evening, 

 flashing forth a greenish light from the under surface 

 of the tail. The light is almost continuous, but it may 

 be seen to wax and wane. It is likely that the sig- 

 nificance of the light is to attract the attention of the 

 males, who fly about vigorously. The light is produced 

 from a yellowish substance inside the tail, which is 

 well supplied with air tubes. Some say that what 

 happens is a rapid burning away or oxidation, while 

 others maintain that there is also a rapid fermentation 

 process, as seems almost certainly the case in the 

 related Fire Flies. It is certain that oxygen and 

 water are essential to the; production of the light. 

 One must not make too much of a mystery of it, for 

 just as rapid changes that go on in our muscles, 



